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CELLS

Plant vs Animal Cells

Plant and animal cells are very similar because they are both eukaryotic cells. They both contain nuclei, mitochondria, endoplasmic reticulum,golgi apparatus, lysosomes, and peroxisomes. Both also contain similar membranes, cytosol, and cytoskeletal elements. The functions of these organelles are extremely similar between the two classes of cells (peroxisomes perform additional complex functions in plant cells having to do with cellular respiration). However, the few differences that exist between plant and animals are very significant and reflect a difference in the functions of each cell.

Functions of parts of a cell

Here are some of the important cell parts and their jobs:

Cell membrane – like the walls of a castle, the cell membrane allows in things that are needed (like food) and allows out things that aren’t needed (like waste).  The cell membrane is the cell’s first line of defence to keep unwanted intruders out (like viruses!).

Cytoplasm – sort of like jelly, the cytoplasm is the cell’s internal environment and keeps the organelles from bumping into each other.

Endoplasmic reticulum (E.R.) – specific jobs vary from one cell type to another, but ultimately helps with transportation of proteins, much like a conveyor belt.

Golgi apparatus – modifies and transports proteins from the E.R., as well as creation of lysosomes and transport of lipids.  The Golgi apparatus is like a factory, it builds and ships.

Lysosome – these sacs are full of enzymes for digesting food that come into the cell.

Mitochondrion – like power plants, the mitochondria turn sugar into energy that’s usable by the cell.  Your house uses electricity, the cell uses a molecule called ATP.

Nuclear envelope – is like a second wall around the nucleus.  Just like the King has a second set of guards closer to him, the nuclear envelope is even more selective than the cell membrane, and not much gets through.  There are holes in the nuclear envelope and usually only nucleic acidsand some proteins are allowed in and out.

Nucleolus – primarily makes ribosomes.  That’s all you need to know!

Nucleus – the mayor’s office of the cell.  Everything that happens in the cell is ultimately controlled by the nucleus and the DNA inside.   The lack of a nucleus is a easy way to tell that the cell you’re looking at is a prokaryote.

Ribosome – take amino acids and make proteins.  It’s like a little machine that runs nonstop until it reaches the end of its job.

Differences between plant and animal cells

 A plant cell has the cell wall which is made of cellulose whereas animal cell doesn’t have cell wall.

 Another comparison can be made based on their shape. A plant cell has fixed rectangular shape whereas animal cell has generally round and irregular shape.

 A plant cell has one large shape vacuole which covers the large part of a cell, the animal cell has one or more vacuole which is much smaller then plant cell. The vacuole is generally a storage unit used to store water in the cell.

 The animal cell doesn’t have chloroplast. A plant cell has chloroplast as they make their own food by photosynthesis. It also imparts a green colour to the plants.

 Nucleus lies on the one side of peripheral cytoplasm in plant cell whereas nucleus lies in the centre of the animal cell.

 Centrioles are present in the animal cell and are usually absent in plant cell. Centrioles help in the formation of the spindle fibres that separate the chromosomes during cell division (mitosis).

Parameters	Animal Cell	Plant Cell
Cell Wall	Absent (only cell membrane)	Present (formed of cellulose)
Shape	Round (irregular shape)	Rectangular (fixed shape)
Vacuole	More than one vacuoles, smaller in size.	One, large central vacuole.
Centrioles	Present in all animal cells	Only present in lower plant forms.
Chloroplast	Animal cells don’t have chloroplasts.	Plant cells have chloroplasts because they make their own food.
Cytoplasm	Present	Present
Plasma Membrane	Only cell membrane	Cell wall and a cell membrane

Experiment:

To observe the structures of a plant cell

The bulb of an onion is formed from modified leaves. While photosynthesis takes place in the leaves of an onion containing chloroplast, the little glucose that is produced from this process is converted in to starch (starch granules) and stored in the bulb.

How to Obtain a Thin Layer of Onion Cells

An onion is made up of layers that are separated by a thin membrane. For this experiment, the thin membrane will be used to observe the onion cells. It can easily be obtained by peeling it from any layer of the onion using tweezers.

How to Prepare a Wet Mount Slide

• A thin onion membrane,
• Microscopic glass slides,
• Microscopic cover slips,
• A needle,
• Blotting paper,
• Dropper,
• Iodine Solution,
• Water,
• Microscope

To avoid breaking the slide and damage to the microscope objective lenses during observation, it is important that the optical tube be lowered to the point that the objective lens is as close to the slide as possible.

This should be done starting with low power while looking from the side of the microscope rather than through the eye piece. From this point, it becomes easier to focus for clarity without any accidents.

1. Add a drop of water at the centre of the microscopic slide
2. Having pulled of a thin membrane from the onion layer, lay it at the center of the microscopic slide (the drop of water will help flatten the membrane)
3. Add a drop of iodine solution on the onion membrane (or methylene blue)
4. Gently lay a microscopic cover slip on the membrane and press it down gently using a needle to remove air bubbles.
5. Touch a blotting paper on one side of the slide to drain excess iodine/water solution,
6. Place the slide on the microscope stage under low power to observe.
7. Adjust focus for clarity to observe.

Students can make another slide without adding the stain to see the difference between a stained slide and a non- stained slide.

Observations

• Large, rectangular interlocking cells,
• Clearly visible distinct cell walls surrounding the cells,
• Dark stained nucleus,
• Large vacuoles at the centre,
• Small granules may be observed inside the cells (within the cytoplasm)

The layers of an onion contain simple sugars (carbohydrates) some of which are stored as starch (starch granules). Given that iodine tends to bind to starch, it stains the starch granules when the two come in to contact making them visible.

Although onions may not have as much starch as potato and other plants, the stain (iodine) allows for the little starch molecules to be visible under the microscope. Although onions are plants, students will not see any chloroplasts in their slides.

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Photosynthesis

·         It is the process by which green plants manufacture their own food

·         They trap sunlight using chlorophyll and convert it to glucose using water & oxygen

·         Oxygen is released as a by product

Equation

                                                Chlorophyll

Carbon dioxide + water                                            Carbohydrates + Oxygen

                                                Sunlight

Raw materials of Photosynthesis

1.       Carbon dioxide

2.       Water

Products of Photosynthesis

1.       Carbohydrates

2.       Oxygen

Conditions necessary

1.       Chlorophyll

2.       Sunlight

Sources of raw materials for photosynthesis

Water – it is sucked from the soil by the roots (osmosis) & transported up the stem to the leaf where it is used

Carbon dioxide– it moves into the leaf from the air by the process of diffusion through the stomata (tinny holes under the leaf)

The Process:- How photosynthesis occurs

Ø  Carbon dioxide and water enter leaf cells

Ø  Chloroplasts in the chlorophyll traps sunlight energy.

Ø  The light energy is s used to split water into hydrogen and oxygen.

Ø  The oxygen escapes from the leaf to the atmosphere as a by-product.

Ø  The hydrogen reacts with carbon dioxide to form carbohydrates.

Structure of the leaf

1.       Cuticle - It is a thin waxy layer at the top of leaf which results in evaporation

2.       Upper epidermis - It is a layer of cells which protects the leaf

3.      Palisade mesophyll layer - These cells contain most of the chloroplasts & carries out most of the photosynthesis

4.      Spongy mesophyll layer - It is a layer of cells with spaces in between them which allows diffusion of carbon dioxide & water. The layer carries out photosynthesis &stores nutrients

5.      Vascular bundle - It contains xylem vessels which carry water and phloem vessels which carry nutrients to plant cells for respiration and to seeds and other storage organs.

6.      Lower epidermis - It is like the upper epidermis but it contains small holes called stomata. These holes control the movement of carbon dioxide into the leaf and oxygen out of leaf. Special cells called guards cells controls the opening and closing of the stoma allowing the gaseous exchange.

Factors needed for photosynthesis

1.       Carbon dioxide

2.       Water

3.      Sunlight

4.      Chlorophyll

Factors affecting the rate of photosynthesis

There are 4 factors affecting the rate of photosynthesis,

1.        Amount of carbon dioxide – increased carbon dioxide increases rate of glucose production which speeds up photosynthesis

2.       Light intensity- light energy is trapped by chlorophyll to split water molecules & therefore increasing light energy will speed up the rate of photosynthesis

3.      Temperature – temperature affect rates of chemical reactions. Low temp makes enzymes inactive & slows down photosynthesis while very high temp will kill the enzymes stopping photosynthesis

4.      Amount of water available – adequate amounts of water are needed & any shortage will slow down photosynthesis

Adaptations of leaves to photosynthesis

1.       Most leaves are broad to maximise the area which absorbs sunlight.

2.       The leaves are thin to allow the penetration of sunlight and easy diffusion of carbon dioxide.

3.      The palisade cells contain many chloroplasts closely packed at the upper surface of the leaf so that they absorb sunlight more efficiently

4.      Spongy cells have spaces between them & the lower epidermis has holes which allow easy gaseous exchange. (gaseous exchange refers to the entry of carbon dioxide from the leaf and the exit of oxygen from the leaf)

5.      The leaves have an extensive network of veins to supply water to the leaf

Importance of photosynthesis

1.       It produces carbohydrates which are food for animals. The plants themselves also manufacture their own food. Therefore, plants are called Producers when looking at food chains and food webs.

2.       Photosynthesis produces oxygen which is used by plants and animals during respiration.

3.      Plants use carbon dioxide during photosynthesis which helps to reduce global warming.

4.      Photosynthesis converts light energy into chemical energy. This chemical energy can be used for many processes in our everyday life e.g. we burn firewood to get heat

What happens to the products of photosynthesis.

What happens to oxygen produced

1.       Most of the oxygen diffuses into the air where it is used by animals in respiration.

2.       Some of the oxygen is used by plants during respiration.

What happens to the carbohydrates.

1.       Some of the carbohydrates produced are used by the plant during respiration

2.       The balance is stored by the plant in seeds, fruits, bulbs or tubers.

Experiments

Experiment 1: Testing a leaf for starch

Materials.

A green leaf from a potted plant which was kept in the dark 3 days, a green leaf of a potted plant which was in the sunlight, a test tube, a beaker, a burner, a stand, water, methylated spirit, iodine solution, a dropper, & a white tile.

Process diagram.

N.B: the methylated spirit is heated in a water bath because it is highly flammable (can easily catch fire easily)

Method

1.       Boil the leaf in water to destroy the enzymes in the leaf, to prevent any chemical reactions

2.       Boil the leaf in alcohol to remove chlorophyll so that results are easy to see

3.      Dip the leaf in hot water to soften it as boiling it in alcohol makes brittle

4.      Place the leaf on a white tile & use a dropper to put the iodine solution on the leaf, iodine solution is used to test for starch & changes colour from brown to blue-black if starch is present

Observation

1.       For the leaf that was kept in the dark for 3 days the iodine solution did not change colour, this means there was no starch. Putting a plant in the dark is called de-starching because darkness stops all photosynthesis & all the starch that had been manufactured is used up

2.       For the plant that was in the sunlight the iodine changed colour from brown to blue black meaning starch was present in the leaf. In science we say the test was positive

Experiment 2: to test if carbon dioxide is necessary for photosynthesis

Materials

1.       2 similar potted plants

2.       10cm³ of soda lime

3.      10cm³ of sodium hydroxide solution

4.      2 bell jars

5.      Starch testing kit

Method

1.       2 similar potted plants are kept in the dark for 3-4 days in order to de-starch them. The starch from their leaves is used up when plant respires in the dark & is not replaced as no photosynthesis can take place without light

2.       Before the experiment ensure that the plants are completely de-starched by testing for starch

3.      Set up the apparatus as shown in the diagram below. Place soda lime and sodium hydroxide as shown by the diagram as these remove co² from the air

4.      Expose both plants to sunlight for 6 hrs & then test a leaf for starch from each plant

Diagram

Observations & Conclusions

1.       When tested for starch the leaf from jar B turned blue – black to show the presence of starch this is because photosynthesis was taking place as all necessary conditions were present, jar B is the control of the experiment

2.       When tested for starch, the leaf from jar A remained brown to prove absence of starch. No photosynthesis was taking place as the soda lime prevented carbon dioxide from the air entering & sodium hydroxide absorbed any carbon dioxide inside the jar. Without carbon dioxide photosynthesis cannot take place

N.B. The stopper on the bell jar is sealed with Vaseline to prevent entrance of carbon dioxide

Experiment 2: testing if light is necessary for photosynthesis

Materials

1.       Potted plant

2.       Aluminium foil

3.      Cello tape

4.      Scissors

5.      Starch testing kit

Method

1.       De- starch the potted plant before the experiment

2.       Take a small piece of foil and cut a simple shade in the middle & cover the leaf with the foil ensuring that the cut shade is on top of the leaf

3.      Leave the potted plant for 6 hrs

4.      Make a sketch of the leaf, taking note of the areas which are completely covered

5.      Remove a leaf from the plant& test it for starch ( use the covered leaf)

Diagram

Observations & Conclusions

1.       The areas which were exposed to sunlight turned blue-black during the starch test to prove that photosynthesis was taking place

2.       The portion which was covered did not have any starch & iodine remained brown this proved that sunlight is necessary for photosynthesis

Experiment 4: testing if chlorophyll is necessary for photosynthesis

Materials

1.       A variegated leaf and a starch testing kit

Method

1.       Make a sketch of the leaf taking note of those areas without chlorophyll

2.       Test the leaf for starch

Diagram

Results & Conclusions

1.       The portions which had chlorophyll had a positive result when tested for starch (iodine turn blue- black)

2.       Those portions which were not green had a negative result when tested for starch. This proves that chlorophyll is necessary for photosynthesis to take place

N.B.  If you do not make a sketch first it will not be possible to remember which parts were green & which parts were white since the whole leaf will be white when boiled in alcohol during the starch test

Experiment 5: To prove that oxygen is produced during photosynthesis

Materials

1.       A water weed

2.       Beaker

3.      Funnel

4.      Test hole

5.      Glowing splint

Method

1.       Pour water into a glass beaker

2.       Place the water weed in the water & invert a short stemmed funnel over it making sure that the stem of the funnel is completely submerged into the water

3.      Fill the test tube with water & and invert it over the stem of the funnel in the water

4.      Place the apparatus in the sunlight for 3 hrs observing what happens

Diagram

Observations

1.       Gas bubbles were seen coming from the weed and collecting in the test tube

2.       The collected gas increased with time pushing the water in the test tube

3.      When the test tube was removed without turning it, a glowing splint was put inside, the splint re-ignited

Conclusions

·         Because the splint ignited, it proves that the gas that was collected was oxygen

N.B: This experiment can be adapted & used to observe the effect of different light intensity levels on photosynthesis.

The apparatus as set up will be put closer or further away from a light source & count the number of gas bubbles produced in each case. More bubbles will be produced if it is put closer to a light source while less bubbles are produced the further the light source will be.

Another variation will be to use bulbs of different power.

In this case the greater the power (the light intensity) the more the number of bubbles produced per minute.

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Human  alimentary canal

The alimentary canal is a long tube which runs from the mouth to the anus. It is part of the digestive system. The digestive system also includes the liver and the pancreas.
Main regions of the alimentary canal and associated organs are:

• Mouth, salivary glands
• Oesophagus
• Stomach
• Pancreas, liver, gall bladder
• Small intestine (duodenum + ileum)
• Large intestine (colon +rectum)
• Anus.

Functions

Mouth – food is taken into the digestive system through the mouth. This is called ingestion. In the mouth the food is broken down into smaller pieces by the teeth. This is a form of physical digestion. The process of chewing also mixes the food with Saliva which has the following functions;

The four main types of teeth are:

·         Incisors - Your incisors are eight teeth in the front center of your mouth (four on both bottom and top). These are typically the first adult teeth that a child will get, coming in  when the child is between six and eight years old. Incisors are the teeth that you use to bite into your food.

·         Canines - Your canines are the next teeth that develop in your mouth. You have four of them and they are your sharpest teeth, used for tearing apart food.

·         Premolars - Premolars are used for tearing and crushing food. Unlike your incisors and canines, premolars have a flat biting surface. You have eight premolars in total.

·         Molars - Your molars are your largest teeth. Their function is similar to that of the premolars, to grind, tear, and crush food. Molars have a large flat biting surface which makes them perfect for this job.

Functions of saliva

1.       It lubricates the food which makes the movement of food in the gullet easy.

2.       Saliva contains an enzyme called Salivary Amylase which converts starch to maltose.

3.      It also provides and alkaline environment which is required for the operation of the enzyme amylase.

The Oesophagus/Gullet

It is a tube which links the mouth to the stomach. Food is moved down this tube by the process called peristalsis. During the process of peristalsis, muscles above the food contract and those below the food relax, pushing the food down the gullet.

The stomach

Food in the stomach is mixed with Gastric juices produced from the walls of the stomach by a process called churning. The juices have the following purposes;

1.       Lubricates the food to make movement easy down the digestive system.

2.       Contains hydrochloric acid which kills bacteria ingested with food and creates the optimum pH for the operation of enzymes.

3.      Contains two enzymes, rennin and pepsin. Rennin coagulates milk while pepsin changes protein to peptides and peptones.

The Duodenum

This is the first section of the small intestines. Pancreatic juice from the pancreas and bile from the gall bladder are added to the food.

Functions of bile

1.       Bile emulsifies (breaks down into smaller particles) fats making their digestion easy.

2.       It also creates the proper pH for the operation of enzymes

Functions of Pancreatic Juice

1.       Contains the following enzymes

a.      Lipase – this breaks down fats to fatty acids and glycerol

b.      Pancreatic Amylase – it breaks down starch to maltose.

c.       Trypsin – it breaks down proteins to peptides and peptones.

The Ileum

This is the second section of the small intestines. The ileum has two major functions, digestion and absorption.

1.       Digestion – juices are added to the food which contain the following enzymes;

a.      Lipase – to digest fats to fatty acids and glycerol

b.      Maltase – maltose to glucose

c.       Peptidases – peptones and peptides to amino acids

d.      Sucrase – sucrose to glucose

e.      Lactase – Lactose to glucose

2.       Absorption – the ileum is very long and contains small finger like structures called villi which are rich in blood vessels. Both the length and the villi are designed to increase the surface area available for the absorption of food substances like glucose and amino acids into the blood stream.

The Colon

Absorption of water, mineral salts and vitamins into the blood stream takes place in the colon. It is also called the large intestines.

The Rectum

Holds undigested remains(faeces) of food before egestion.

The Anus – The purpose of the anus is egestion. This is the passing out of waste food substances from the body.

Other Organs supporting the digestive system.

The liver

The liver is important for the following reasons;

1.       The liver produces bile and it is stored in the gall bladder.

2.       It regulates levels of sugar in the blood by converting excess glucose to glycogen and later converting the glycogen back to glucose when sugar level fall.

3.      The liver also breaks down excess proteins into urea and uric acid to excreted out of the body as urine.

The Pancreas

Pancreatic juice flows into the duodenum. It contains enzymes that digest starch, proteins and lipids, and contains sodium hydrogen-carbonate to partly neutralise the acidity of food coming from the stomach.

Absorption is the movement of digested food molecules through the wall of the intestine into the blood by the process of diffusion. 

Significance of Villi Villi are finger like projections that increase the surface area for absorption. If a section of small intestine was turned inside out, its surface would be kike a carpet. Inside each villus are:
            - Blood capillaries: absorb amino acids and glucose.
            - Lacteals: absorb fatty acids and glycerol.

Food molecules are absorbed:  - mainly by diffusion or by active transport. Active uptake makes use of energy.

Role of the hepatic portal vein 

The hepatic portal vein transports absorbed food from the small intestine to the liver. After a meal, the blood in this vein contains very high concentrations of glucose and amino acids, as well as vitamins and minerals. The liver reduces levels backs to normal levels required by the body. 

The absorbed nutrients are carried to the liver in the hepatic portal vein. Some are used in the liver, some are stored, and some are sent on in the blood to be delivered to cells all over the body.

Assimilation

This is the use of the absorbed food substances in the body by body cells. Glucose is used during the process of respiration; Protein is used for growth and repair of wounds and mineral salts for protection against diseases.

The use of the end products of Digestion

Glucose

1.       Excess glucose is converted by the liver and is stored.

2.       Excess also converted into fats and are stored around organs and under the skin.

3.      Glucose is used to release energy during the process of respiration.

Glucose + Oxygen                                                                              Carbon dioxide + Water + Energy

                   Insulin

Glucose                                                                                            Glycogen

 

                   Adrenalin

Amino Acids

1.       Used for the formation (synthesis) of protein e.g. making new cells, enzymes, hormones and repair of worn out tissues.

2.       Excess amino acids are broken down into urea and uric acid by the liver and excreted out of the body as urine.

Fatty acids and glycerol

1.       Are burnt to provide energy to the body especially when glucose is in short supply.

2.       Some are made into cell membranes

3.      Excess are converted to fats which insulates the body providing warmth, and protect organs such as the heart and the intestines.

Mechanical digestion is the physical process of preparing the food for chemical digestion.

• It involves chewing (in the mouth), mixing, churning (in the stomach and intestine) and segmentation (in the intestine).

• Large pieces of food are breaking down into smaller pieces à increases the surface area of the food.

• Bile physically digests fats by emulsifying them – turning them into small droplets with a large surface area.

Chewing

Mechanical digestion, performed by the teeth à pieces of food are mixed with saliva and become smaller and easier to swallow and have a larger surface area.

Peristalsis

• The walls of the alimentary canal have an inner, circular muscle fibre coat and an outer, longitudinal muscle fibre coat.
• As the ball of food (bolus) formed in the mouth enters the pharynx, a reflex action is initiated.
• This produces slow, wave-like contractions in the walls of the oesophagus and later along the whole length of the tract (peristalsis).
• Peristaltic waves involve the contraction of the circular muscle fibres behind the bolus (A) and their relaxation in front of the bolus.
• Longitudinal muscles provide the wave-like action. The two functions together push the ball down the tract (B).

Chemical digestion 

• Involves breaking down large, insoluble molecules into small, soluble ones.
• Enzymes speed up the process. They work efficiently at body temperature (370 C) and at suitable pH.
• The main places where chemical digestion happens are the mouth, stomach and small intestine.

Effect of Different Temperatures on the Activity of Salivary Amylase on Starch

Materials Required

Three series of test tubes having iodine solution in each, test tubes, ice cubes, water, 15 ml 1% starch solution + 3 ml 1% sodium chloride, saliva solution, droppers, thermometer, Bunsen burner and wire gauze.

Procedure

• Take beaker containing 15 ml of 1% starch solution + 3 ml of 1% sodium chloride solution.
• Divide and pour this solution into three test tubes and mark them as A, B and C.
• Maintain the temperature of the beaker containing ice cubes at 5°C.
• Take beaker containing ice cubes and keep it on the table.
• Take another two beakers containing water and heat over the Bunsen burner.
• Now transfer experimental tube A into a beaker containing ice.
• Transfer the second experimental tube B into water bath set at 37°C and third experimental tube C into the beaker maintained at 50°C.
• Using a dropper, take 1 ml saliva solution and transfer the solution into test tube A.
• Similarly, add 1 ml saliva solution into test tube B and test tube C.
• Immediately, using a dropper, take few drops from experimental tube A and transfer this into first series of test tubes having iodine solution.
• Similarly, using fresh droppers, do the same procedure for test tube B and test tube C and transfer the solution into second and third series of test tubes having iodine solution.
• Note this time as zero-minute reading.
• After an interval of 2 minutes, again take a few drops from each tube and add to the iodine tubes and note the change in colour of iodine.send
• Keep on repeating the experiment at an interval of every 2 minutes till colour of iodine does not change.

Results

It takes less time to reach achromic point at 37°C, as the enzyme is maximum active at this temperature, while at higher and lower temperatures more time is taken to reach theachromic point.

Conclusion

All enzymes are proteinaceous in nature. At lower temperatures, the enzyme salivary amylase is deactivated and at higher temperatures, the enzyme is denaturated. Therefore, more time will be taken by enzyme to digest the starch at lower and higher temperatures. At 37° C, the enzyme is most active, hence, takes less time to digest the starch.

Effect of Different pH on the Activity of Salivary Amylase on Starch

Materials Required

Three series of test tubes having iodine solution in each, test tubes, pH tablets of 5, 6.8 and 8, beaker containing water with thermometer, 15 ml 1% starch solution + 3 ml 1% sodium chloride, saliva solution, droppers, Bunsen burner and wire gauze.

Procedure

• Take a beaker containing 15 ml of 1% starch solution + 3 ml of 1% sodium chloride solution.
• Divide and pour this solution into three test tubes and mark them as A, B and C.
• Add pH tablet 5 into test tube A, pH tablet 6.8 into test tube B and pH tablet 8 into test tube C.
• Now transfer experimental tube A, B and C into a beaker containing water and a thermometer for recording temperature. Temperature of this beaker is to be maintained at 37°C.
• Using a dropper, take 3 ml saliva solution and add 1 ml of solution to each of the three test tubes.
• Immediately using a dropper, take few drops from experimental tube A and transfer this into the first series of test tubes having iodine solution.
• Similarly, do the same procedure for test tube B and test tube C and transfer the solution into second and third series of test tubes having iodine solution.
• Note this time as zero-minute reading.
• After an interval of 2 minutes, again take a drop from each tube and add to the iodine tubes and note the change in colour of iodine.
• Keep on repeating the experiment at an interval of every 2 minutes till colour of iodine does not change.

Results

pH 5 is acidic and pH 8 is alkaline, therefore salivary amylase did not act in these tubes. Whereas, the enzyme acted in the tube with pH 6.8 (i.e., slightly acidic) and digested the starch.

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Mineral Nutrition in plants

·         Apart from the products of photosynthesis plants also need mineral elements from the soil

·         These elements are found dissolved in water in the soil

·         In natural ecosystems, they are usually adequately available but agricultural soils sometimes have a deficiency and will need to be added

·         Nitrogen, phosphorous & potassium are the 3 major elements required by plants for healthy growth

·         Some elements like iron, calcium, magnesium & zinc are required but in very small amounts and are called trace elements

Nitrogen (N)

·         Nitrogen is essential for plant growth & reproduction

·         It is needed by plants for building up proteins

·         A plant with adequate nitrogen has good leaf growth & looks healthy and green

Nitrogen deficiency symptoms

1.       Stunted or poor growth

2.       The yellowing of leaves

3.      Poor quality seeds

How to correct nitrogen deficiency

Shortage of nitrogen in the soil can be corrected by:

·         Addition of manure or compost

·         Addition of fertilisers in the form of nitrates and compounds

·         Crop rotation

Phosphorous (P)

·         It is important for root development & seed germination

·         It is also used in all plant activities that require energy

Symptoms of deficiency

·         The leaves become purple

·         Poor root development

·         Tall thin plants

Correction of deficiency in the soil

·         Phosphorous is supplied in the form of soluble phosphate in the fertilisers e.g. ammonium phosphate

Potassium (K)

·         It is important for flowering and fruit formation

·         It is also necessary for the neutralisation of organic acids in plants & helps during the uptake of mineral salts from the soil (active uptake)

Deficiency symptoms

1.       Yellowish or brown leaf margins

2.       Poor flowering & fruiting

3.      Premature death of plant

Correction of deficiency

·          Addition of fertilisers e.g. compound D

Experiment 1: to test the effects of nitrogen, phosphorous, and potassium on plants

Materials

1.       Bean seedlings

2.       5 test tubes

3.      Mineral solutions

4.      Aluminium foil or black paint cotton wool

Method

1.       Take 5 test tubes or small bottles & label them A to E and fill them all with water cultures as follows:

·         Test tube A- put the complete culture solution containing nitrogen, phosphorous, & potassium

·         Test tube B – put distilled water

·         Test tube C- put culture solution with phosphorous & potassium

·         Test tube D-  put culture solution with nitrogen & phosphorous

·         Test tube E-put culture solution with nitrogen & potassium

2.       All the test tubes should be covered with aluminium foil or painted black. This is done to prevent sunlight from entering the solution and so avoid the growth of algae which may affect mineral content

3.      In each test tube place 5 bean seedlings which are more or less identical which are surrounded by cotton wool to support them

Diagram

Observations and conclusion

1.        Plant A is the control, it has the necessary elements for plant growth

2.       Plant B has a poor plant growth as there are no nutrients in the water

3.      C has got a yellow margined leaf

4.      D has brown leaf margins & premature death of plant

5.      Plant E there is no root development and seed germination therefore the leaves become purple and the plant become thin and tall.

Plant pests and diseases

·         A pest is an insect or any organism that damages plants or grains

·         Common agricultural pests include mammals (rodents, mammals) birds & insects

·         The most serious of pests are the insects which damage both crops & livestock

Examples of plant pests and the damage they cause

1.       Tissue eating pests- these have biting jaws & use these to eat plant parts, symptoms include chewed leaves and holes in the plant for example cutworms, locusts, grasshoppers, cricket, caterpillars e.t.c. Their mouths parts are called mandibles

2.       Sap sucking pests – mouth parts stuck into the leaves to suck out sap. The leaves become distorted, shrunken and discoloured. They destroy the plant by removing essential sap from the plant, examples aphids and red spider mite. They mouth parts are called stylets 

Examples of plant diseases

1.       Bacteria wilt – this is a disease caused by bacteria, plants will start wilting even though water is abundantly available. This is caused by the accumulation of bacteria in xylem vessels breaking the movement of water. They may appear as nodules on plant roots.

2.       Fungal rust- this is caused by microscopic fungi leaving in the stems and leaves of plants. Rust red spots appear on leaves hence the name fungal rust

3.      Powdery mildew – also caused by microscopic fungi and leaves are coated with a light powder

Why control pests and diseases

1.       Plants pests and diseases reduce the yields of crops, this is because they reduce the surface area available for photosynthesis or slow down plant growth.

2.       In extreme cases plant pests can destroy crops threatening food security and causing losses to farmers.

Methods of pest control

There are 3 main methods which are used to control pests:

1.       Cultural control

2.       Biological control

3.      Chemical control

Cultural control

·         Involves the use of good farming practises which make more difficult for a pest to establish itself, example include

1.       Early planting-plants grow strong before the numbers of pests have multiplied

2.       Weed control-removes hiding places for pests and reduces their population

3.      Crop rotation- same crops are easily attached by certain pests which may remain dormant in the soil after the harvest. If the next crop is of the same family the dormant pest will be able to attach it, however if the different family is planted the dormant will not be able to attack the new plant

4.      Clean planting environment-cuttings and seeds used for planting should be used free of pests before being used. The fields should be fumigated and last season crop remains should be removed since there may be keeping pests

5.      Healthy farming- organic manure and fertilisers make crops grow strong so that they can resist the attack of pests and diseases

6.      Burning or burying- farmers may burn or bury maize stocks after harvest. This kills maize stock borers which would otherwise lie dormant during the dry season. The disadvantage of this method is that it also destroys insects that are not pests & therefore disturbs the balance of nature

Examples of cultural control in cotton

One of the main types of pests to attack cotton is the bore worm, which can survive from one season to the next as the pupa stage leaving in the soil. Rotating the cotton crop with maize which is not a food source for bore worm is recommended as the pupa will die from lack of food when a maize crop is planted.

The pest will either find a new cotton field or it will die. Another cultural control method for cotton is the closed season after harvesting. Nothing is sawn on the cotton field for at least 2 months. This makes the soil insects suffer from lack of food and die leaving the soil pest free for the next crop.

It is important to remove all remaining green plants after harvest to make sure that the pest larvae do not survive. Most farmers burn the stocks. In Zimbabwe, it is illegal to have unclear fields after the close of the cotton and tobacco season.

Biological control

This involves the introduction of parasites & predators which are the natural enemies of the pests that need to be destroyed e.g. a plant called the African marigold has been known to reduce nematodes population in the soil. Another biological method can be to pick off the large insects from plants and then kill them; the major disadvantage of bio control is that the new organisms may start to attack crops that have been previously resistant to attack.

Chemical control

It can be used to prevent pests. A pesticide is applied to the pest to stop the pest from attacking them, if a pest attack has just begun pesticides can be applied to kill the pest at various stages of their life cycle. Pesticides can be supplied as solution or dust sprays to the plant part or organ affected by the pest or disease

Precautions for the use of chemicals

1.       Keep chemicals in secure cardboards away from children & away from food & medicines

2.       Read & follow instructions on labels when using a chemical

3.      Wear protective clothing such as gloves, face, musk etc.

4.       Avoid smoking or eating while using chemicals

5.      Chemicals should be stored only in their original containers & all empty containers & all empty containers should be disposed of quickly & safely

Effects of pesticides on pests

1.       Stomach poisoning pesticide- these kill pests that eat sprayed crops

2.       Systematic pesticides- these are absorbed by the crops & if any pest eat or suck sap juices from the plant, it is killed.

3.      Contact poison pesticides- kills any pest which comesn into contact with the chemical on the user & the 

Disadvantages

1.       Some of the methods involve hard work e.g. uprooting individual cotton plants

2.       Burning – destroys even harmless insects

Biological control

Advantage

1.       It is cheap

Disadvantage

1.       A new pest maybe attracted by the predator introduced

Chemical control

Advantage

1.       It is a chemical which is effective because it kills all pest on the plant

Disadvantage

1.       It is an expensive method

2.       Introduces poisonous to the environment & is dangerous to the user

3.      Kills harmless insects.

Respiration and Gaseous Exchange

We will begin this topic by looking at experiments first, then close by looking at the human respiratory system and its functions.

1 EXPERIMENT

COMPARING INHALED AND EXHALED AIR

MATERIAL

-Beakers, small pipes, limewater

METHOD

-BLOW IN AND OUT THROUGH THE PIPE

RESULTS

-The limewater in ‘A’ turn milky white  in ‘B’ remains the same.

CONCLUISION

-carbon dioxide is present in ‘A’, thus inhaled air has carbon dioxide

RESPIRATION

-The process whereby glucose is broken down to release energy in the presence of oxygen.

-Occurs inside the cells of living organisms, during the process, carbon dioxide and water are released.

WORD EQUETION

GLUCOSE+OXYGEN              CARBONDIOXIDE+WATER+HEAT ENERGY

-the process is known as aerobic respiration

-the energy produced is used for moving and other activities

-oxygen is used up and carbon dioxide released.

2. EXPERIMENT

-WHICH GAS IS RELEASED DURING RESPIRATION

MATERIALS

-small animal e.g. rat, frog; limewater; three test tubes; potassium hydroxide; glass/rubber tubing

METHOD

-Set up the apparatus as shown in the diagram

-the apparatus compare the amount of carbon dioxide in inhaled and exhaled air

DIAGRAM

RESULTS

-limewater in ‘B’ turned milky white and that in ‘A’ remained clear

CONCLUISION

-limewater in ‘B’ turned milky white because the carbon dioxide concentration is high.

COMPARING RESPIRATION AND PHOTOSYNTHESIS

RESPIRATION	PHOTOSYTHESIS
Catabolic-carbohydrates are broken down.	Anabolic- carbohydrates are manufactured
Oxygen is taken in	Oxygen is taken in
Carbon dioxide is given off	Carbon dioxide is taken in
Energy is released	Energy is absorbed and stored

3 EXPERIMENT

TO SHOW THAT HEAT IS PRODUCED DURING RESPIRATION

MATERIAL

-two thermo flasks; germinating seeds; cotton wool; thermometers

METHOD

1.       Divide the germinating seeds into two equal sets

2.       Boil one set and disinfect it

3.      Place the two sets of seeds and thermometers into the thermo flasks

4.      Record temperature at the beginning and after 30 minutes

RESULTS

-      The temperature in ‘A’ will be higher than ‘B’ because dead seeds do not germinate

CONCLUISION

-      Germinating seeds produce heat through respiration.

Gaseous exchange

·         is the physical process to get oxygen into the lungs and waste gases as carbon dioxide out of the blood.

The human respiratory system

It starts from the mouth and nose down through the trachea/windpipe to the bronchus and is further passed to the bronchioles to air sacs/ alveoli.

                   

The Alveoli

The role of the alveoli

·         these are the air sacs through which gaseous exchange takes place in the lungs.

·         They are numerous and their large surface area is good for intake of oxygenated air and expulsion of deoxygenated air.

·         The lining of the alveoli is semi permeable (allowing air only to pass through).

·         Capillaries surrounding the alveolus contain less oxygen than present in the air sac, thus oxygen diffuse through into the capillaries.

·         Carbon dioxide is more in the capillaries than in the air sacs, thus diffuse through into the air sacs.

Functions of parts of the respiratory system.

1.       VOICE BOX

-Is held open by the trachea to allow passage of air

2.       TRACHEA

-      Is a cartilage structure

-      Lining has cilia which are in constant motion and traps dust and dirt

-      It also helps in moisturising air

3.      BRONCHUS AND BRONCHIOLES

-      Channels air to and from the alveoli

-      Containing mucus and cilia to trap dust and micro organisms

4.      ALVEOLI

-      These are small thin walled semi permeable air sacs

-      They are numerous and provide a large surface area for gaseous exchange; this ensures that sufficient oxygen is obtained.

5.       Ribs

-      Protect lungs

-      Are raised during inhalation and lowered to reduce volume and expel waste gases during exhalation

Differences between inhaled and exhaled air

SUBSTANCE	INHALED AIR	EXHALED AIR
OXYGEN	20%	16%
CARBON DIOXIDE	0.03%	4%
WATER	Usually dry	Usually moist(high)
TEMPERATURE	Lower than exhaled air	Higher than inhaled
NITROGEN	79%	79%
GERMS	Has	Usually does not have
DUST PARTICLES	Has	Does not have

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