Nutrition in Plants

Question 1

Structure and components of chloroplasts

Answer 1

They are double-membraned cell organelles, with both membranes known as the chloroplast envelope
The fluid inside a chloroplast is known as stroma
Chlorophyll is found in the thykloid sacs, and stacks of thykloids are called granum

Question 2

What light is useful for photosynthesis?

Answer 2

Visible light

Question 3

What pigments take in light for photosynthesis?

Answer 3

Chlorophyll takes in all visible light except green
(a is the most important, b is the accessory)

Carotenoids are yellow and orange accessory pigments
They absorb different wavelengths of light from chlorophyll, expanding the spectrum of light that provides energy for photosynthesis

Question 4

Define photosynthesis

Answer 4

Photosynthesis is the process in which green plants TRAP/ABSORB light energy and convert it into chemical energy for the formation of carbohydrates and its subsequent uses

Question 5

Word and chemical equation of photosynthesis

Answer 5

Carbon dioxide + Water ——(sunlight and chlorophyll)——> Glucose and Oxygen

6CO2 + 6H2O ——> C6H12O6 + 6O2

Question 6

What happens to the glucose plants make during photosynthesis?

Answer 6

Since glucose is the raw material of respiration, mitochondria in plant cells use glucose to RELEASE energy, which is then used for growth and repair
Excess glucose can be stored as starch
Glucose can also be converted into surprise for transport to other parts of the plant

Question 7

Why are most life forms completely dependant on photosynthesis?

Answer 7

The sun is the ultimate source of energy, and the process of photosynthesis allows light energy from the sun to be converted into chemical energy (food)
Photosynthesis provides food and energy to animals and humans
Photosynthesis removes carbon dioxide (raw material of photosynthesis) and produces oxygen gas (end product of photosynthesis) which can be used by organisms for aerobic respiration)

Question 8

Where do the raw materials and conditions of photosynthesis come from?

Answer 8

Carbon dioxide molecules enter the stomata on the leaves via diffusion
Water molecules are absorbed at the roots and transported to leaves.

Chlorophyll is found in the thykloid sacs of chloroplasts

Question 9

What happens during the light dependant stage of photosynthesis?

Answer 9

Light energy is absorbed by chlorophyll
It is converted into chemical energy or used in photolysis of water (a raw material of photosynthesis) is split into H+ ions and oxygen
It occurs in the thylakoids of chloroplasts

Question 10

What happens during the light independent stage (Calvin cycle) of photosynthesis?

Answer 10

The H+ ions from the light dependant stage are used to reduce the CO2 into C6H12O6 (glucose), via a series of enzymatic reactions
Occurs in the stroma (space outside thylakoids) of the chloroplasts
Also known as the Calvin cycle

Question 11

List all the parts of a leaf

Answer 11

Tip, lamina, midrib, margin, vein, petiole

Question 12

How is the leaf externally adapted to carry out photosynthesis?

Answer 12

The leaf blade or lamina is flattened and thin, allowing quick diffusion of carbon dioxide into the cells of the leaf due to short distance to travel. Large surface area also allows more sunlight to be absorbed.

The leaf stalk or petiole positions the leaf away from the stem, exposing it to maximal amounts of sunlight.

The network of veins consists of vascular bundles, made up of xylem and phloem. Xylem transports water to the leaves (raw material of photosynthesis), while the phloem transports sucrose (product of photosynthesis) away from the leaf to other parts of the plant.

Question 13

Describe the internal leaf structure and where the vascular bundles are found

Answer 13

Consists of 4 main layers of cells:
Upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis
Vascular bundles consisting of xylem and phloem tissues are found in the mesophyll layers

Question 14

What is the upper epidermis?

Answer 14

The uppermost layer of cells
Functions to revise mechanical support to the leaf
Transparent, allow sunlight to pass through into mesophyll layers
Coated with waxy and waterproof cuticle, reducing water loss via evaporation
Do not contain chloroplasts, one cell layer thick

Question 15

What is the palisade mesophyll?

Answer 15

The second layer in the leaf
Contains columnar-shaped cells, closely packed together, less air spaces
Large number of chloroplasts to ensure maximal sunlight absorption
Majority of photosynthesis takes place here
Multiple cell layers thick

Question 16

What is the spongy mesophyll?

Answer 16

Third layer in the leaf
Contains many irregularly shaped cells, many intercellular air spaces allowing for quick diffusion of gases (eg. CO2) into photosynthetic cells
Cells covered in a thin layer of water, for CO2 to dissolve
Chloroplasts present, but less than palisade mesophyll
Multiple cell layers thick

Question 17

What is the lower epidermis?

Answer 17

Fourth and lowest cell layer of the leaf
Function to provide mechanical support to the leaf
Chloroplasts absent
Guard cells (2 form 1 stoma) are found here
One cell layer thick

Question 18

Where are chloroplasts found?

Answer 18

Palisade mesophyll, spongy mesophyll, guard cells (in lower epidermis)

Question 19

What are guard cells?

Answer 19

Bean-shaped chloroplast-containing cells in lower epidermis, controlling the opening and closing of the stoma (plural: stomata)
They have an uneven cell wall, where the inner wall is thicker than the other wall, creating the bean shape

Question 20

What are stomata?

Answer 20

The site of gaseous exchange in plants
They allow CO2 to diffuse in and O2 to diffuse out of the leaf
The loss of water through the stomata of the leaves is known as transpiration

Question 21

What happens to stomata at high light intensities? (During photosynthesis)

Answer 21

The water potential of the guard cells is more negative
Osmosis occurs, water moves from the surrounding lower epidermal cells (region of less negative water potential) into the guard cells (region of more negative water potential), across a partially permeable membrane (guard cell’s cell membrane)
The entry of water causes the guard cells to become turgid, opening the stomata, allowing for more gaseous exchange.

Question 22

What happens to stomata at lower light intensities?

Answer 22

The water potential of the guard cells is less negative.
Osmosis occurs, water moves from the guard cells (region of less negative water potential) to the surrounding lower epidermis cells (region of more negative water potential) across a partially permeable membrane (guard cell’s cell membrane)
The exit of water causes the guard cells to become flaccid, causing them to close to decrease the rate of transpiration and prevent water loss

Question 23

Describe the starch test on leaves

Answer 23

1. Place leaf in boiling beaker of water, killing it and stoping all enzymatic reactions including photosynthesis
2. Leaf is placed in boiling tube filled with ethanol and placed in hot water bath (not boiling, ethanol is flammable), so leaf decolourises and changes from green to white
3. Leaf is placed in hot water to soften it
4. A few drops of iodine solution is added to test for presence of starch

Question 24

Where do the two stages of photosynthesis occur?

Answer 24

Light dependent stage: thylakoids

Light independent stage: stroma

Question 25

Why can’t plants photosynthesis with green light?

Answer 25

Leaves reflect green light, so no light energy can be taken in, which is a condition for photosynthesis