chapter 17 p2

Question 1

Chemiosmosis:

Answer 1

The ATP produced in both photosynthesis and respiration is synthesised primarily by a process called chemiosmosis.

it involves the diffusion of protons from a region of high concentration to a region of low concentration through a partially permeable membrane.

The movement of the protons as they flow down their concentration gradient releases energy that is used in the attachment of an inorganic phosphate (Pi) to ADP, forming ATP.

Chemiosmosis depends on the creation of a proton concentration gradient.

The energy to do this comes from high-energy electrons (excited electrons).

Question 2

Electrons are raised to higher energy levels, or excited, in two ways:

Answer 2

electrons present in pigment molecules (e.g., chlorophyll) are excited by absorbing light from the Sun

high energy electrons are released when chemical bonds are broken in respiratory substrate molecules (e.g.. glucose).

The excited electrons pass into an electron transport chain and are used to generate a proton gradient.

Question 3

Electron transport chain:

Answer 3

An electron transport chain is made up of a series of electron carriers, each with progressively lower energy levels.

As high energy electrons move from one carrier in the chain to another, energy is released.

This is used to pump protons across a membrane, creating a concentration difference across the membrane and therefore a proton gradient.

The proton gradient is maintained as a result of the impermeability of the membrane to hydrogen ions.

Question 4

flow of electrons down an electron transport chain diagram

Answer 4

Question 5

The only way the protons can move back through the membrane down their concentration gradient is through…

Answer 5

hydrophilic membrane channels linked to the enzyme ATP synthase (catalyses the formation of ATP).
The flow of protons through these channels provides the energy used to synthesise ATP (from ADP and P)

Question 6

chemiosmosis in photosynthesis and respiration

Answer 6

In photosynthesis, ATP is used to synthesise glucose and other organic molecules.
The ATP produced in respiration provides the energy needed by metabolic processes and reactions essential to life.
A simple way of modelling this process is to think of the flow of water through a hydroelectric power station causing turbines to spin, generating electricity.
Both chemiosmosis and hydroelectric power generation result in energy in a very useable form.

Question 7

two processes also vital in chemiosmosis

Answer 7

The processes of oxidative phosphorylation (in respiration) and photophosphorylation (in photosynthesis)

Question 8

Photosynthesis is the process by which

Answer 8

energy, in the form of light from the Sun, is used to build complex organic molecules, such as glucose.

Light energy is transformed into chemical energy trapped in the bonds of the complex organic molecules produced.

Question 9

autotrophic

Answer 9

Organisms that can photosynthesise, like plants and algae

Question 10

Heterotrophic organisms

Answer 10

like animals, obtain complex organic molecules by eating other (heterotrophic and/or autotrophic) organisms.

Question 11

Both autotrophic and heterotrophic organisms then…

Answer 11

break down complex organic molecules during the process of respiration to release the energy they need to drive metabolic processes.

Question 12

Structure and function of chloroplasts:

Answer 12

photosynthesis takes place in chloroplasts.

The network of membranes present within chloroplasts provides a large surface area to maximise the absorption of light essential in the first step of photosynthesis.

The membranes form flattened sacs called thylakoids which are stacked to form grana (singular granum)

The grana are joined by membranous channels called lamellae.

Light is absorbed by complexes of pigments, such as chlorophyll, which are embedded within the thylakoid membranes.

The fluid enclosed in the chloroplast is called the stroma and is the site of the many chemical reactions resulting in the formation of complex organic molecules.

Question 13

Pigment molecules

Answer 13

absorb specific wavelengths (colours) of light and reflect others.
Different pigments absorb and reflect different wavelengths and this is why they have different colours.
The primary pigment in photosynthesis is chlorophyll.

Question 14

Chlorophyll

Answer 14

absorbs mainly red and blue light and reflects green light.
The presence of large quantities of chlorophyll is the reason for the familiar green colour of plants.
Although there are a number of different pigments that absorb light, the primary pigment is chlorophyll a.

Question 15

Other pigments

Answer 15

chlorophyll b, xanthophylls, and carotenoids absorb different wavelengths of light than those absorbed by chlorophyll a.
Different combinations of pigments are the reason for the different shades and colours of leaves.
Chlorophyll b, xanthophylls, and carotenoids are embedded in the thylakoid membrane of the chloroplast.
These and other proteins and pigments form a light harvesting system (also known as an antennae complex).

Question 16

The role of the light harvesting system

Answer 16

is to absorb, or harvest, light energy of different wavelengths and transfer this energy quickly and efficiently to the reaction centre.

Question 17

reaction centre

Answer 17

where chlorophyll a is located

where the reactions involved in photosynthesis take place.

Question 18

photosystem.

Answer 18

what the light harvesting system and reaction centre are collectively know as

Question 19

digram of a photosystem

Answer 19

Question 20

inside of a leaf diagram

Answer 20

Question 21

chloroplast structure diagram

Answer 21

Question 22

grana and thylakoids diagram

Answer 22

Question 23

absorption spectrum

Answer 23

Question 24

Plants need light to photosynthesise but if sunlight is too intense…

Answer 24

chlorophyll is destroyed.
Chlorophyll has to be continuously synthesised during the summer to maintain the level needed to photosynthesise at the required rate.

Question 25

Chlorophyll is not produced when

Answer 25

there is little or no sunlight - this is why areas of grass that have been covered turn yellow.

Question 26

Carotenoids

Answer 26

accessory pigments responsible for the yellow/orange colours seen in plant leaves.
Orange carotene and yellow xanthophyll are two examples.
These colours are not normally seen because they are masked by the green colour of chlorophyll.
Carotenoids are not broken down, unlike chlorophyll, in strong sunlight and are present throughout the growing season.
The shorter days and cooler nights of autumn cause changes in the pigment composition in leaves.
Chlorophyll a is no longer produced and leaves turn yellow/orange as we see the carotenoids.

Question 27

Anthocyanin

Answer 27

is a red/purple pigment formed from a reaction between sugars and proteins present in cell sap.

It is produced when the concentration of sugars is high.
High light intensity also promotes the production of anthocyanins.

produces the red skin of apples and the purple of black grapes.

The colour of the anthocyanin pigments is pH-dependent, leading to a range of different colours from red to purple.

act as a sunscreen by absorbing blue-green and ultraviolet light, thereby inhibiting the destruction of chlorophyll.

In their role as pigments they help trees maximise production towards the end of the growing season as the weather changes in autumn.

The red/purple coloration of leaves is also thought to camouflage leaves from herbivores blind to red wavelengths.

Question 28

Investigating photosynthetic pigments:

Answer 28

Chromatography can be used to separate the different pigments in a plant extract.

The mobile phase would be the solution containing a mixture of pigments and the stationary phase a thin layer of silica gel applied to glass.

The different solubilities of the pigments in the mobile phase, and their differing interactions with the stationary phase, lead to them moving at different rates.

This results in the pigments being separated as they move through the silica gel.

Question 29

The retention value (Rf) for each pigment can be calculated using the formula:

Answer 29

Question 30

The two stages of photosynthesis:

Answer 30

Light-dependent stage
energy from sunlight is absorbed and used to form ATP
Hydrogen from water is used to reduce coenzyme NADP to reduced NADP.

Light-independent stage
hydrogen from reduced NADP and carbon dioxide is used to build organic molecules, such as glucose.
ATP supplies the required energy

Question 31

diagram of the light-dependent stage

Answer 31

Question 32

diagram of the light-independent stage

Answer 32