Photosynthesis

Question 1

Site of photosynthesis

Answer 1

The leaf is the main photosynthetic structure in eukaryotic plants.
Chloroplasts are the organelles where it occurs.

Question 2

Adaptations of the lead for photosynthesis

Answer 2

• large surface
• arrangement of leaves to minimise overlapping & therefore shadowing
• thin so most light is absorbed
• transparent cuticle and epidermis
• long, narrow upper mesophyll cells packed with chloroplasts
• lots of stomata so gas exchange and mesophyll cells are close
• stomata open and close in response to light intensity
• many air spaces for rapid diffusion
• network of xylem to bring water to leaf and phloem to carry it away

Question 3

Equation for photosynthesis

Answer 3

6CO2 + 6H2O —> C6H12O6 + 602

Carbon dioxide + water -> glucose + oxygen

Question 4

What is photosynthesis

Answer 4

A process of energy transferral

Light energy is conserved in chemical bonds

Question 5

3 main stages of photosynthesis

Answer 5

1) capturing of light energy by chlorophyll
2) light dependent reaction
3) light independent reaction

Question 6

Structure and role of chloroplasts in photosynthesis

Answer 6

Vary in shape and size. Usually disc shaped and 2-10um long and 1um diameter. Surrounded by double membrane.

• grana. Stacks of 100 discs called thylakoids. Thylakoids gave chlorophyll and some gave tubular extensions that join up thylakoids in adjacent to grana called intergranal lamelle
• stroma. Fluid filled matrix (LIR occurs)containing structures e.g. Starch grains

Question 7

Where do light dependent reactions occur

Answer 7

In thylakoids membranes of chloroplasts

In membranes are light harvesting systems called photosystems

Question 8

What is the aim of light dependent reactions

Answer 8

To produce ATP and reduced NADP to drive light independent reactions

Question 9

Factors of oxidation

Answer 9

• gain of oxygen
• loss of electrons
• substance becomes oxidised
• loss if hydrogen(protons)
• energy given out

Question 10

Factors of reduction

Answer 10

• loss of oxygen
• gain if electrons
• substance becomes reduced
• gain if hydrogen (protons)
• energy taken in

Question 11

What is photoionisation

Answer 11

Electrons leave the chlorophyll molecule

Occurs because they become excited by the absorption of light energy

Question 12

What is chemiosmosis

Answer 12

The theory of circulation of protons through thylakoids membrane (via ATP synthase) to produce ATP and reduced NADP

Question 13

What is ATP synthase

Answer 13

An enzyme that makes ATP

Question 14

What is photophosphorylation

Answer 14

Name of the way in which the ATP is being made

Question 15

Photolysis

Answer 15

Occurs in thylakoids space
Uses up water
Products are protons, electrons and oxygen
The protons and electrons-> reduce NADP, oxygen - given off as a byproduct or used in respiration

Question 16

Stages of the light dependent reaction

Answer 16

1) in the thylakoid membranes are proteins called electron carriers which are arranged in a chain in a sequence
2) electrons released from Chlorophyll pass down the carriers which is called the electron transfer chain
3) if the carrier has an electron it is said to be reduced. When the electron leaves the carrier, the carrier is said to be oxidised
4) as the electrons pass from one carrier to the next, some of the energy released is used to pump a proton(H+) into thylakoid space
5) the proton concentration in the thylakoid space is further increased by photolysis
6) a concentration gradient of protons is set up
7) protons can only move back through the thylakoid membrane by ATP synthase enzymes
8) as the protons move back through they generate the production of ATP from ADP plus a pi
9) NADP on the stroma side of the membrane combines with protons and electrons to form reduced NADP

Question 17

Where does the light independent reaction take place

Answer 17

In the stroma of chloroplasts

Question 18

What is the light independent reaction also called

Answer 18

Calvin cycle

Question 19

Stages of the light independent reaction

Answer 19

1) CO2 from atmosphere diffuses into leaf through stroma and dissolves in water around walls of mesophyll cells. It then diffuses to cell surface membrane, cytoplasm and chloroplast membranes into stroma of chloroplasts.
2) in stroma, CO2 reacts with RuBP (catalysed by rubisco) to produce 2 molecules of 3-carbon GP
3) reduced NADP reduces GP to TP using energy from ATP
4) NADP is re-formed and goes back to LDR to be reduced again by accepting more protons
5) TP molecules are converted to organic substances that the plant requires such as starch, cellulose, lipids, glucose, amino acids and nucleotides

Question 20

How many times must the LIR turn to make a whole molecule of glucose?

Answer 20

6