Nutrition in Plants Flashcards
What is the basic knowledge required to do photosynthetic experiments?
- Glucose is first formed from carbon dioxide during photosynthesis.
- Presence of starch in the leaves suggests that photosynthesis has taken place.
Expl: When glucose is formed more quickly than it is used up, the excess glucose is changed to starch for storage.
Action to take: Test for starch using the iodine test - Destarching (removal of starch) must be carried out on the plants before the experiments.
Expl: This ensures that starch is absent in the leaves prior to the experiments.
Thus, all starch present in the leaves after the experiments must have been formed during the experiments.
Action: Put the plants in the dark for two days.
In darkness, photosynthesis stops and enzymes in the leaves change starch to sucrose, which is transported to other parts of the plants.
What happens during photosynthesis?
In the light-dependent stage:
-Light energy is absorbed by chlorophyll and then converted into chemical energy.
-Light energy is also used to split water molecules into oxygen and
hydrogen atoms. This is called photolysis of water.
In the light-independent stage:
-The hydrogen produced in photolysis is used to reduce carbon dioxide to carbohydrates such as glucose.
-Enzymes play a part in both light-dependent and light-independent stages.
What is the word equation for PS?
carbon dioxide + water —–> glucose + oxygen
What happens to the glucose that is formed during
photosynthesis?
- USED IMMEDIATELY
-for cellular respiration to provide energy for cellular activities
-to form cellulose cell walls - STARCH IN LEAVES
-in daylight, the rate of photosynthesis is so great that sugars are formed faster than they can be removed. The excess glucose is
converted into starch.
- in darkness, photosynthesis stops and starch is converted by enzymes back into glucose - CONVERTED TO SUCROSE
-Transported to other parts of plant or to storage organs, for example, seeds, stem tubers or root tubers via phloem.
- Converted to starch or other forms of storage compounds at the storage organs
-Might be converted back to glucose - USED TO FORM PROTEINS
- Glucose reacts with nitrates and other mineral salts absorbed from the soil to form AA, to form proteins.
for synthesis of new protoplasm in the leaves or for storage as proteins - FORMS FAT
-For storage
-Use for cellular respiration.
-For synthesis of new protoplas.#m
Why is photosynthesis important?
- Photosynthesis makes chemical energy available to animals
and other organisms - Photosynthesis removes carbon dioxide and provides oxygen
- Energy is stored in fossil fuels through photosynthesis
What is the function of the upper epidermis?~
The upper epidermis is covered on the outside by a waxy and transparent cuticle.
Which Reduces water loss through evaporation from the leaf; transparent for light to enter the leaf.
What is the function of the Mesophyll Layer?
It is the main site of photosynthesis. The mesophyll consists of two types of tissue — palisade mesophyll and spongy mesophyll.
How do guard cells control the size of stomata?
SUNLIGHT
- The guard cells photosynthesise, converting light energy to chemical energy.
- The chemical energy is used to pump potassium ions (K+) into the guard cells from neighbouring epidermal cells.
- Water potential of the guard cells is lowered.
- Water from neighbouring epidermal cells then enters guard cells by osmosis.
- This increases the turgidity of the guard cells and causes them to become swollen.
- The guard cells have a thicker cell wall on one side of the cell (the side around the stomatal pore).
- This causes the swollen guard cells to become more curved and pull the stoma open.
How do guard cells control the size of the stomata?
NIGHTTIME
- The potassium ions that have accumulated in the guard cells during the day diffuse out of the guard cells.
- Water potential in the guard cells is increased.
- Water leaves the cells by osmosis.
- The guard cells become flaccid and the stoma closes.
How does carbon dioxide enter the leaf?
- In daylight when photosynthesis occurs, the carbon dioxide in the leaf is rapidly used up. The carbon dioxide concentration in the leaf becomes lower than that in the atmospheric air, so a diffusion gradient exists. Therefore, carbon dioxide diffuses from the surrounding air through the stomata into the air spaces in the leaf.
- The surfaces of the mesophyll cells are always covered by a thin film of water so that carbon dioxide can dissolve in it.
- The dissolved carbon dioxide then diffuses into the cells.
How does water enter the leaf?
- The xylem transports water and dissolved mineral salts to the leaf from the roots.
- Once out of the veins, the water and mineral salts move from cell to cell right through the mesophyll of the leaf.
