Biology Revision

Created by: Sophie
Created on: 17-05-11 10:33

All About Plants

Plants need CO2 and H20 for photosynthesis. This a process of which plants can produce their own food called Glucose. During photosynthesis the chloroplasts (contains chlorophyll, a green pigment that absorbs the energy from sunlight), in the plant's leaves, absorbs light from the sun, it uses CO2 and water from the soil to produce oxygen and glucose as products. Glucose is a sugar and is used by the plant for food, oxygen is a waste product and so diffuses out of the leaves.

CO2+water-->glucose and oxygen

Plants use this Glucose for other things than food: Synthesis: Glucose combines with minerals from the soil to make compounds. Nitrogen and Glucose combine to produce proteins. Magnesium and Glucose combine to make Chlorophyll. Storagee: Glucose that is not immediatley used by the plant is converted into insoluble starch for storge. Respiration: Respiration is a process used by all living cells to release energy from Glucose. This energy is used to make the molecules required for growth. Plants can use the glucose they produce. Cellulose: Hundreds of Glucose molecules join together to make Cellulose. Its used to make Cell Walls, which help support the plant.

The presence of starch in a leaf shows us that the plant has synthesised. We can use iodine to test this. It reacts with and changs colour from brown to blue-black. The starch test can prove that plants need light and chlorophyll to take place. How do test: Boil a leaf for 30 seconds-this kills cyptoplasm and softens cell walls, making the leaf permeable to iodine. Place leaf in a test tube of Ethanol, this extracts chlorophyll from the leaf-easier to see colour change. Place leaf in a beaker of warm water, this softes the leaf, and then place a few drops of iodine onto the leaf and see if the colour changes.

Chlorophyll cannot be removed from a plant without killing it so instead variegated(Leaves that do not have a uniform colour are called variegated leaves) leaves can be used to show Chlorophyll is essential for photosynthesis. These leaves contain pale parts, which do not contain Chlorophyll, the green parts of the leaf contain Chlorophyll and are the control.

Factors tat affect the rate: Light/CO2/Temperature. Light energy has to be absorbed by chlorophyll. The brighter the light the more energy, therefore, the faster the reaction. If light intensity is too high plant cells can be damaged and the enzymes denatured. CO2 is used by plants to make food. The more of it, the faster the rate of reaction and so they will grow more quickly. Temperature, if the temperature gets too hot (above 40 degrees) the enzymes can become denatured this can make the rate of photosynthesis slow down, or even stop. If one of these factors are restricted, the rate of photosynthesis will be below the maximum rate. These factors control how quickly photosynthesis occurs. It is called a limiting factor.

Leaves are adapted.