Chapter 7 - Nutrition In Plants

Question 1

Define autotrophs.

Answer 1

Organisms like plants that are able to synthesise their food by process of photosynthesis.

Question 2

What are 5 Conditions necessary for photosynthesis?

Answer 2

1) sunlight
2) water
3) carbon dioxide
4) suitable temperature
5) chlorophyll

Question 3

Describe an experiment that proves that sunlight is necessary for photosynthesis.

Answer 3

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.

Question 4

Describe an experiment which proves that chlorophyll is necessary for photosynthesis.

Answer 4

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.

Question 5

Why are plants green?

Answer 5

Chlorophyll absorbs mainly red and blue light, thus the plant reflects green light and appears green to us.

Question 6

Describe an experiment which proves that carbon dioxide is necessary for photosynthesis.

Answer 6

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.

Question 7

Define photosynthesis.

Answer 7

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.

Question 8

What is the overall chemical equation of photosynthesis?

Answer 8

6 CO2 + 12 H2O —>(light energy+chlorophyll) C6H12O6 + 6 O2 + 6 H2O

Question 9

Where does photosynthesis occur?

Answer 9

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.

Question 10

Describe the role of a chlorophyll.

Answer 10

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.

Question 11

What happens during the light stage?(3)

Answer 11

1) absorption of light energy by chlorophyll
2) conversion of light energy to chemical energy
3) photolysis of water (break down using light)

Question 12

What are the 2 equations for the light stage?

Answer 12

1) light energy —>(chlorophyll) chemical energy (ATP).

2) 12 H2O —-> (photolysis of water) 6 O2 + 24 H

Question 13

What happens during the dark stage(light independent)?

Answer 13

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.

Question 14

What is the equation of the dark stage?

Answer 14

6 CO2 —>(enzyme-controlled reaction - chemical energy and hydrogen atoms) C6H12O6 + 6 H2O

Question 15

List 4 differences between the light-dependent and light-independent stage.

Answer 15

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.

Question 16

Name 3 factors affecting the rate of photosynthesis.

Answer 16

1) light intensity
2) CO2 concentration
3) temperature

Question 17

Define limiting factors.

Answer 17

A factor that directly affects or limits a process if its quantity or concentration is altered is called a limiting factor.

Question 18

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?

Answer 18

Beyond the point, light is no longer a limiting factor as the maximum rate of enzymatic activity in chloroplast has been reached.

Question 19

Describe and explain the effects of increasing temperature on rate of photosynthesis.

Answer 19

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.

Question 20

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?

Answer 20

Beyond the point, carbon dioxide concentration is no longer a limiting factor as the maximum rate of enzymatic activity in chloroplast has been reached.

Question 21

What is the fate of glucose in leaves?(5)

Answer 21

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

Question 22

Why is photosynthesis important? (3)

Answer 22

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.

Question 23

What is the function of the lamina/leaf blade?

Answer 23

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.

Question 24

What is the function of the petiole(leaf stalk)?

Answer 24

Positions lamina for maximum absorption of sunlight and gaseous exchange.

Question 25

What are 2 functions of veins?

Answer 25

1) allow transport of water and mineral salts to cells in lamina.
2) transport manufactured food from leaves to other parts of the plant

Question 26

What is the function of the regular arrangement of the leaves?

Answer 26

Ensure leaves are not blocking one another from sunlight and that each leaf receives optimum amount of light.

Question 27

What is the function of the cuticle? (2)

Answer 27

1) waxy, impermeable layer above the epidermis prevents excessive water loss due to evaporation
2) transparent to allow sunlight to penetrate to the mesophyll

Question 28

What is an epidermis? What is its function?

Answer 28

single layer of closely packed epidermal cells with no chloroplast. Its main function is to protect inner cell from injuries.

Question 29

What is a palisade mesophyll and what is its function?

Answer 29

A few layers if closely packed cells which are long, cylindrical. Its contains numerous chloroplasts for maximum absorption of light for photosynthesis.

Question 30

What is a spongy mesophyll and what are its 2 functions?

Answer 30

They are irregularly shaped cells.

1) main: numerous large intercellular air spaces allows for rapid diffusion of gases inside the leaf
2) sub: photosynthesis but not as good as cuticles

Question 31

What is the function of the vascular bundle?

Answer 31

Presence of xylem and phloem allows the transport of food materials and water respectively within the plant.

Question 32

What is the lower epidermis? What is its function?

Answer 32

1) single, protective layer of cells

2) presence of stomata for gaseous exchange

Question 33

How do guard cells regulate the size of the stomata in the day?(3)

Answer 33

1) guard cells photosynthesize, converting light energy to chemical energy. The chemical energy is used to pump K+ ions into the guard cells from neighboring epidermal cells
2) water potential of guard cells is lowered. Water from neighboring epidermal cells then enters the guard cells by osmosis. This increases the turgidity of the guard cells, causing them to become swollen.
3) guard cells have a thicker wall on one side of the cell. This causes the swollen guard cells to become more curved and pull the stoma open.

Question 34

How do guard cells regulate the size of the stomata at night?

Answer 34

At night, K+ ions diffuse out of the guard cells. Water potential in guard cells increases, leading to the exit of water via osmosis. Guard cells become flaccid and stomata closes.

Question 35

What is the function of the guard cell?(2)

Answer 35

1) Regulate the opening and closing of stomata for exchange of gases in the leaf via diffusion.
2) contain chloroplasts for photosynthesis

Question 36

Why can a stomata still close during the day?

Answer 36

To reduce water loss. Excess evaporation of water will cause guard cells to become flaccid.

Question 37

How do carbon dioxide enter the leaf?(4)

Answer 37

1) CO2 is rapidly used up during photosynthesis.
2) thus, the CO2 concentration inside the leaf is lower than the atmospheric air, setting up a concentration gradient.
3) CO2 diffuses from surrounding air into the air spaces in the leaf via the stomata.
4) CO2 dissolves into the thin film of water surrounding mesophyll cells, and then diffuse into cells.

Question 38

How do water enter leaves?

Answer 38

Water is brought into the leaves via xylem vessels in veins. Water leaves the veins and moves from cell to cell in the mesophyll by osmosis.