Chapter 7 - Nutrition In Plants Flashcards
Define autotrophs.
Organisms like plants that are able to synthesise their food by process of photosynthesis.
What are 5 Conditions necessary for photosynthesis?
1) sunlight
2) water
3) carbon dioxide
4) suitable temperature
5) chlorophyll
Describe an experiment that proves that sunlight is necessary for photosynthesis.
1) destarch a plant by putting it in the dark for 2 days. Test for presence of starch using a leaf.
2) sandwich another leaf which is still attached to the plant between two pieces of black paper and place it in strong sunlight.
3) test the leaf for starch a few hours later. Only the parts exposed to sunlight will be stained blue-black;sunlight is necessary.
Describe an experiment which proves that chlorophyll is necessary for photosynthesis.
1) a plant with variegated leaves is destarched by placing it in the dark for 2 days.
2) place it in strong sunlight for a few hours.
3) a leaf is removed, decolorized and tested for starch. Only those parts containing chlorophyll will manufacture starch and be stained blue-black.
Why are plants green?
Chlorophyll absorbs mainly red and blue light, thus the plant reflects green light and appears green to us.
Describe an experiment which proves that carbon dioxide is necessary for photosynthesis.
1) destarch 2 potted plants by placing them in the dark for 2 days.
2) enclose them in polythene bags to ensure the microoganisms does not release CO2. Put KOH solution in one of the set-ups to remove CO2.
3) after a few hours, remove a leaf from each pot and test for presence of starch. Iodine only turns blue-black for leaf exposed to air with CO2.
Define photosynthesis.
Photosynthesis is the process in which light energy is ABSORBED by chlorophyll is converted into chemical energy. The chemical energy is used to synthesis glucose from water and CO2, which are the raw materials for photosynthesis. Oxygen is released during the process.
What is the overall chemical equation of photosynthesis?
6 CO2 + 12 H2O —>(light energy+chlorophyll) C6H12O6 + 6 O2 + 6 H2O
Where does photosynthesis occur?
In the green leaves, there is a mesophyll layer. In the cytoplasm of the mesophyll cells, there is an organelle called chloroplast that contains green pigment chlorophyll that is embedded in the thylakoid membranes.
Describe the role of a chlorophyll.
It is a green pigment that absorbs light energy and converts it to chemical energy. This chemical energy is used to produce organic carbohydrate, glucose, from inorganic carbon dioxide and water during photosynthesis.
What happens during the light stage?(3)
1) absorption of light energy by chlorophyll
2) conversion of light energy to chemical energy
3) photolysis of water (break down using light)
What are the 2 equations for the light stage?
1) light energy —>(chlorophyll) chemical energy (ATP).
2) 12 H2O —-> (photolysis of water) 6 O2 + 24 H
What happens during the dark stage(light independent)?
1) Hydrogen atom produced from photolysis of water and chemical energy is used to reduce CO2 to form glucose by a series of enzyme reactions.
2) glucose formed is used for respiration and formation of cellulose cell walls
3) glucose is converted into sucrose and transported to storage organs via translocation
4) excess glucose is stored as starch or fats, and converted into proteins to form new protoplasm.
What is the equation of the dark stage?
6 CO2 —>(enzyme-controlled reaction - chemical energy and hydrogen atoms) C6H12O6 + 6 H2O
List 4 differences between the light-dependent and light-independent stage.
1) the light-dependent stage (LD) requires light energy, water and chlorophyll, while the light-independent stage (LI) requires carbon dioxide, enzymes, chemical energy and Hydrogen atoms
2) in LD, light is absorbed by chlorophyll and converted into chemical energy while in LI, energy required is from LD and enzymes are involved to catalyse reactions.
3) in LD, only photolysis - light energy from sunlight used to split water molecules into O2 and H2 atoms occurs, while in LI, Hydrogen from photolysis is used to reduce CO2 to form glucose.
4) the products of LD include H2 atoms, oxygen and ATP(storage form of energy), while products of LI include glucose and water.
Name 3 factors affecting the rate of photosynthesis.
1) light intensity
2) CO2 concentration
3) temperature
Define limiting factors.
A factor that directly affects or limits a process if its quantity or concentration is altered is called a limiting factor.
In a light intensity graph, after a certain point, the rate of photosynthesis remains the same even though light intensity increases. What does this imply?
Beyond the point, light is no longer a limiting factor as the maximum rate of enzymatic activity in chloroplast has been reached.
Describe and explain the effects of increasing temperature on rate of photosynthesis.
1a) at low temperature, rate of photosythesis is slow.
1b) enzymes are inactive
2a) as the temperature rises, every 10C doubles the rate of reaction(only write if no graph)
2b) increases in kinetic energy, more collision, more enzyme-substrate complex formed
3a) at optimum temperature, rate of photosynthesis is the highest
3b) enzymes most active
4a) beyond optimum temperature, rate of photosynthesis decreases sharply.
4b) enzymes are denatured. Hydrogens bond break, they lose 3 dimensional shape and active site. Enzymes can no longer bind onto substrate and thus no enzyme-substrate complex is formed.
In a carbon dioxide concentration graph, after a certain point, the rate of photosynthesis remains the same even though carbon dioxide concentration increases. What does this imply?
Beyond the point, carbon dioxide concentration is no longer a limiting factor as the maximum rate of enzymatic activity in chloroplast has been reached.
What is the fate of glucose in leaves?(5)
1) used immediately by plant cells for cellular respiration or to form cellulose cell walls
2) excess glucose is temporarily stored as starch in leaves.
3) converted into sucrose when there is a need to transport it to storage organs.
4) reacts with nitrate and mineral salts to form amino acids which are combined to form proteins. Excess amino acids are transported away for synthesis of new protoplasm or for storage as proteins.
5) used to form fats for storage
Why is photosynthesis important? (3)
1) plants are the producers in food chains. The chemical energy stored in plants is transferred to other organisms through feeding.
2) helps purify air by removing CO2 from atmosphere and releasing oxygen as a by-product.
3) coal formed from trees provides a source of fuel.
What is the function of the lamina/leaf blade?
the lamina or leaf blade has a large surface area to maximize sunlight absorption. It allows rapid diffusion of carbon dioxide to reach the inner cells of the leaf.
What is the function of the petiole(leaf stalk)?
Positions lamina for maximum absorption of sunlight and gaseous exchange.
