Photosynthesis

Question 1

What is the xylem?

Answer 1

it transports water to the cells of the leaf.

Question 2

What is the phloem?

Answer 2

it transports sugars to and from the cells of the leaf.

Question 3

What is the spongy mesophyll?

Answer 3

this layer has air spaces to allow a large surface area for gas exchange.

Question 4

What is the waxy cuticle?

Answer 4

this is a thin layer to prevent water loss from the plant, it is transparent to let light through.

Question 5

What is the palisade mesophyll?

Answer 5

this layer is packed with cells that contain a lot of chloroplasts which have chlorophyll for photosynthesis.

Question 6

What is the stoma?

Answer 6

it allows gases in and out and water is lost via this part.

Question 7

What are guard cells?

Answer 7

they control the size of the stoma.

Question 8

What is the chloroplast made up of?

Answer 8

it has a double membrane, contains grama, stroma, lamellae, thylakoids, starch grains and genetic material. It is 2-10 micrometres long and 1 micrometre in diameter and is disk shaped.

Question 9

What is the grana?

Answer 9

it is 100 disc thylakoids stacked up, within the thylakoids is the pigment chlorophyll and it is used in the light dependent stage of photosynthesis.

Question 10

What is the stroma?

Answer 10

it has a fluid filled matrix, within the stroma there are a number of starch grains and is used in the light independent stage of photosynthesis.

Question 11

What is the equation for photosynthesis?

Answer 11

6CO2 + 6H20 —> C6H1206 + 602.

Question 12

What are the three main stages involved in photosynthesis?

Answer 12

• the capturing of light
• the light dependent stage
• the light independent stage

Question 13

What happens in the capturing of light?

Answer 13

Light is absorbed by the pigment chlorophyll which is present in the chloroplasts.

Question 14

Briefly what happens in the light dependent stage of photosynthesis?

Answer 14

Light energy is converted into chemical energy. An electron flow is created and causes the photolysis of water into protons, electrons and oxygen. This stage produces NADPH, ATP and O2.

Question 15

Briefly what happens in the light independent stage of photosynthesis?

Answer 15

Protons are used to reduce the CO2 to produce sugars and other organic molecules.

Question 16

What happens in oxidation?

Answer 16

It is a:

• gain of oxygen
• loss of hydrogen
• loss of electrons

Question 17

What happens in reduction?

Answer 17

It is a:

• loss of oxygen
• gain of hydrogen
• gain of electrons

Question 18

When do oxidation and reduction occur?

Answer 18

Together.

Question 19

What is photoionisation?

Answer 19

a process where chlorophyll absorbs light energy and becomes reduced due to the loss of electrons.

Question 20

What is oxidation?

Answer 20

A process where a substance gains an oxygen or loses a hydrogen.

Question 21

What is reduction?

Answer 21

a process where a substance loses an oxygen or gains a hydrogen.

Question 22

What is chemiosmosis?

Answer 22

The flow of H+ ions from a higher concentration to a lower concentration.

Question 23

What is photolysis?

Answer 23

A process where a water molecule is split by light into H+ ions and OH- ions.

Question 24

What two parts make up the light dependent stage of photosynthesis?

Answer 24

• making ATP

- photolysis of water

Question 25

Making ATP?

Answer 25

a chlorophyll molecule absorbs light which boosts a pair of electrons to a higher energy level. These excited electrons leave the chlorophyll and are taken up by electron carriers. This is the first of a sequence of redox reactions. The chlorophyll is oxidised and electrons are reduced. Next the electrons are passed along a series of electrons carriers in a stage known as the electron transport chain. As the electrons go along the electron carriers they lose energy, this energy is used to synthesis ATP. As the initial energy was derived from light the formation of ATP is called photophosphorylation. When the light struck the chlorophyll, two electrons were lost, these needed to be replaced or the chlorophyll can no longer absorb light. They are replaced in the light dependent stage.

Question 26

Photolysis of water?

Answer 26

As well as exciting electrons in the chlorophyll light energy is also able to split water molecules It yields hydrogen ions, oxygen and electrons. The electrons produced are used to reduce the chlorophyll molecule restoring the electrons it lost. The oxygen produced if a by-product which is either used in respiration or it leaves the cell.

Question 27

What are the products from the light dependent stage?

Answer 27

• NADPH
• Oxygen
• ATP

Question 28

What occurs in the light independent stage?

Answer 28

This stage occurs without light but relies on things created during the light dependent stage. Carbon dioxide from the atmosphere enters the leaf via the stomata and dissolves in water around the mesophyll cells. It can then diffuse into the cell into the chloroplasts stroma. Carbon dixoide reacts with RuBP and it catalysed by the enzyme rubisco and it produces two molecules of GP. NADPH from the light dependent reaction is used to reduce GP to two molecules of TP using energy supplied from ATP. NADP is reformed and returns to be used in the light dependent reactions again. Some of the TP molecules are converted into organic substances such as glucose, starch, cellulose, lipids and amino acids. Most of the TP is used to regenerate the RuBP using ATP from the light dependent reaction. This is known as the Calvin Cycle.

Question 29

What factors limit photosynthesis?

Answer 29

• light intensity
• temperature
• carbon dioxide concentration

Question 30

How does light intensity affect photosynthesis?

Answer 30

As light intensity increases so can the rate of photosynthesis.

Question 31

How does temperature affect photosynthesis?

Answer 31

Low temperatures and high temperatures can be limit photosynthesis.

Question 32

How does carbon dioxide concentration affect photosynthesis?

Answer 32

Low concentrations of carbon dioxide limit photosynthesis.

Question 33

What are the optimum conditions for photosynthesis?

Answer 33

• high light intensity of a certain wavelength
• temperature around 25 degrees
• carbon dioxide at 0.4%
• water

Question 34

How is high light intensity an optimum condition for photosynthesis?

Answer 34

Light is needed to provide the energy for the light dependent reaction, the higher the intensity of the light, the more energy it provides. Only certain wavelengths of light are used for photosynthesis. The photosynthetic pigments; chlorophyll A, chlorophyll B and carotene only absorb the red and blue light from sunlight.

Question 35

How is a temperature around 25 degrees an optimum condition for photosynthesis?

Answer 35

Photosynthesis involves enzymes, ATP synthase and rubisco. If the temperature falls below 10 degrees the enzymes become inactive, but if the temperature is more than 45 degrees they may start to denature. Also at high temperatures the stomata close to avoid losing too much water, this causes photosynthesis to slow down because less carbon dioxide enters the leaf when the stomata are closed.

Question 36

How is carbon dioxide at 0.4% an optimum condition for photosynthesis?

Answer 36

Carbon dioxide makes up 0.04% of the gases in the atmosphere. Increasing this to 0.4% gives a higher rate of photosynthesis but any higher and the stomata begin to close.

Question 37

How is the presence of water an optimum condition for photosynthesis?

Answer 37

Plants also need a constant supply of water, to little and photosynthesis has to stop but too much and the soil becomes waterlogged, reducing the uptake of minerals such as magnesium which is needed to make chlorophyll A.

Question 38

What is the compensation point?

Answer 38

The amount of carbon dioxide given out by respiration is the same as the amount of carbon dioxide taken up by photosynthesis.

Question 39

How is plant growth increased?

Answer 39

Agricultural growers try to create an environment where plants get the right amount of what they need increasing plant growth and yield. They create the optimum conditions in glasshouses by adding carbon dioxide to the air by burning propane, by having lamps which provide light at night and by having heaters and coolers in order to keep a constant optimum temperature and air circulation systems which make sure the temperature is even throughout the glasshouse.