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Question 1

Define the term limiting factor in the context of photosynthesis.

Answer 1

A limiting factor is a factor that limits the rate of photosynthesis.

Question 2

What are the three factors that limit the rate of photosynthesis?

Answer 2

The three limiting factors for photosynthesis are:

temperature

light intensity

carbon dioxide concentration

Question 3

Why does the rate of photosynthesis slow down at low temperatures?

Answer 3

Photosynthesis occurs slowly at low temperatures because molecules (such as enzymes involved in photosynthesis) have little kinetic energy. This means that fewer successful collisions take place.

Question 4

Why do very high temperatures cause photosynthesis to stop?

Answer 4

At very high temperatures the enzymes that control photosynthesis denature, meaning that the reaction can no longer take place.

Question 5

What is the effect of increasing light intensity on the rate of photosynthesis?

Answer 5

The higher the light intensity, the faster the rate of photosynthesis

Question 6

True or False?

The rate of photosynthesis increases consistently as temperature increases. (Higher Tier Only)

Answer 6

False.

The rate of photosynthesis only increases with temperature up to a certain point, after which higher temperatures lead to a decrease in the rate of photosynthesis. This is because high temperatures denature enzymes involved in the reactions of photosynthesis.

Question 7

Answer 7

The equipment shown in the image can be used to investigate the effect of light intensity on the rate of photosynthesis.

Question 8

Answer 8

To measure the rate of photosynthesis we need to know the volume of gas collected and time period during which it has been collected.

Question 9

Answer 9

The independent variable is light intensity, which is controlled by altering the distance between the lamp and the beaker.

Question 10

Answer 10

The dependent variable in this investigation is the rate of photosynthesis, which is measured by recording the volume of oxygen produced within a set time period

Question 11

Answer 11

Control variables for this investigation would include:

maintaining the same environmental temperature

using the same species, length and age of plant in each repeat

dissolving sodium hydrogen carbonate (NaHCO3) in the water to maintain carbon dioxide levels

Question 12

What is the role of root hair cells?

Answer 12

Root hair cells absorb water and minerals from the soil.

Question 13

How are root hair cells adapted to aid the absorption of water and mineral ions?

Answer 13

Root hair cells are adapted for absorption as follows:

they have a large surface area

they contain mitochondria which release energy for active transport

Question 14

True or False?

Minerals move into root hair cells by osmosis.

Answer 14

False.

Mineral ions move into root hair cells by active transport. Only water can move by osmosis.

Question 15

Why do root hair cells need energy from respiration?

Answer 15

Root hair cells need energy to fuel the active transport of mineral ions from the soil against a concentration gradient.

Question 16

How does water move into root hair cells?

Answer 16

Water moves into root hair cells by osmosis.

Minerals, and other dissolved substances, in the cytoplasm of root hair cells lower the water concentration, so water moves into the cells down a water concentration gradient.

Question 17

Define the term xylem.

Answer 17

Xylem are vessels that transport water and mineral ions from the roots to the upper parts of plants.

Question 18

How are xylem vessels adapted to transport water around plants?

Answer 18

Xylem vessels are adapted for water transport as follows:

lignin strengthens xylem cell walls to prevent breakage of vessels

they are hollow and have no end walls to allow continuous water movement

Question 19

Define the term phloem.

Answer 19

The phloem is a tissue that transports dissolved sucrose around the plant.

Question 20

How is phloem tissue adapted for its role?

Answer 20

Phloem tissue is adapted as follows:

phloem tissue contains living cells that supply energy for sucrose transport

it contains elongated tubes along which dissolved sugars can flow

the end walls of cells contain pores to allow passage of dissolved sugars

Question 21

What is the function of the spongy mesophyll in a leaf?

Answer 21

The spongy mesophyll is the region of the leaf where gas exchange takes place. Gases are exchanged between the cells of the spongy mesophyll layer and the surrounding air spaces.

Some photosynthesis also occurs here.

Question 22

True or False?

The air spaces in a leaf are an adaptation for gas exchange.

Answer 22

True.

The air spaces increase the surface area of the leaf that is in contact with the air. Gases can diffuse in and out of the spongy mesophyll cells from and into the air spaces.

Question 23

What is the function of stomata in leaves?

Answer 23

Stomata are small pores present in the epidermis of leaves that allow the movement of gases into and out of leaves by diffusion.

Question 24

What are some adaptations of leaves for gas exchange?

Answer 24

Adaptations of leaves for gas exchange include:

they are thin, reducing the diffusion distance for gases

they are large and flat, increasing their surface area

stomata allow gases to move in and out

air spaces around mesophyll cells increase the contact between cells of the leaf and the surrounding air

Question 25

True or False? The role of the waxy cuticle is to reduce water loss from leaves by evaporation.

Answer 25

True. The waxy cuticle is a waterproof layer that reduces water loss by evaporation from the surface of leaves.

Question 26

How is the palisade mesophyll layer adapted to maximise photosynthesis?

Answer 26

The palisade mesophyll layer contains tall, thin cells that pack together closely. These cells contain many chloroplasts to maximise light absorption.

Question 27

Why is it beneficial for leaves to be broad while having a thin cross-section?

Answer 27

It is beneficial for leaves to be broad and thin because: being broad maximises surface area for light absorption being thin reduces diffusion distance for gas exchange

Question 28

How can the leaves of plants be adapted for survival in extreme conditions?

Answer 28

Adaptations for survival in extreme conditions found in leaves include: reduced surface area reduced number of stomata stomata in pits or surrounded by hairs thickened waxy cuticle rolled-up leaf shape

Question 29

Answer 29

Adaptations for living in dry conditions shown by the cactus include: leaves are reduced to spines to reduce water loss by transpiration thick waxy cuticle reduces water loss by evaporation extensive roots maximise water absorption from the soil a thickened stem allows water storage

Question 30

Define the term transpiration.

Answer 30

Transpiration is the loss of water vapour from the leaves of plants by evaporation. This drives the upward movement of water and mineral ions through plants.

Question 31

How are water and dissolved minerals transported through plants?

Answer 31

Water and dissolved minerals are transported upwards in the xylem. Water is drawn upwards in a continuous column to replace the water lost by evaporation in the leaves.

Question 32

Describe the structure of stomata.

Answer 32

The stomata are pores in the leaf surface, surrounded by two guard cells.

Question 33

What is the role of the stomata and guard cells in transpiration?

Answer 33

The stomata and guard cells allow plants to regulate the volume of water lost during transpiration. When water availability is low the guard cells can close, reducing transpiration.

Question 34

By what process does water vapour exit the leaf air spaces?

Answer 34

Water vapour exits the leaf air spaces by the process of diffusion.

Question 35

Which environmental factors can affect the rate of transpiration in plants?

Answer 35

Factors that affect the rate of transpiration include: light intensity wind speed / air movement temperature Transpiration rate can also be affected by humidity.

Question 36

What happens to transpiration rate as light intensity increases?

Answer 36

As light intensity increases the transpiration rate increases.

Question 37

True or False? Transpiration rate increases as wind speed increases.

Answer 37

True. As wind speed increases the transpiration rate increases.

Question 38

Why does transpiration occur faster on a windy day?

Answer 38

Transpiration is faster on a windy day because wind blows water vapour away from the surface of leaves, maintaining a water vapour concentration gradient between the inside and the outside of leaves.

Question 39

What happens to transpiration rate as temperature decreases?

Answer 39

As temperature decreases the transpiration rate decreases.

Question 40

True or False? Transpiration rate increases at higher temperatures due to the increased kinetic energy of molecules.

Answer 40

True. At higher temperatures water molecules have more kinetic energy and are more likely to diffuse out via the stomata.

Question 41

Answer 41

A bubble potometer works to measure transpiration rate as follows: a bubble is introduced into a tube containing a cut plant stem as the plant transpires water is pulled up the stem, causing the bubble to move the distance the bubble moves in a given time indicates the transpiration rate

Question 42

How can the results of a potometer investigation be used to calculate transpiration rate in a plant shoot?

Answer 42

The results of a potometer investigation can be used to calculate transpiration rate as follows: rate of transpiration = distance moved by bubbledivided bytime

Question 43

Define the term translocation.

Answer 43

Translocation is the movement of dissolved sucrose through phloem tissue.

Question 44

Why does phloem tissue contain living cells with many mitochondria?

Answer 44

The living cells in phloem tissue release energy from their mitochondria. This allows them to move sucrose into the phloem by active transport so that translocation can occur.

Question 45

Why do plants produce plant hormones?

Answer 45

Plants produce hormones in order to coordinate and control growth and development.

Question 46

Why do plants need to respond to stimuli such as light and gravity?

Answer 46

Plants need to respond to stimuli to ensure that they can maximise their growth, e.g. responding to light ensures their leaves can absorb maximum light energy for photosynthesis responding to gravity ensures that shoots grow upwards towards light and roots grow downwards towards water and mineral ions

Question 47

Define the term phototropism.

Answer 47

Phototropism is the directional growth of plants in response to light, allowing shoots to grow towards light to optimise photosynthesis.

Question 48

Define the term gravitropism (or geotropism).

Answer 48

Gravitropism, also known as geotropism, is the directional growth response of plants in relation to gravity; roots grow downwards and shoots grow upwards.

Question 49

True or False? Unequal distribution of auxin results in uneven growth in plant shoots and roots.

Answer 49

True. Auxin distributes itself unevenly in shoots and roots due to the direction of light and gravity. This uneven auxin distribution results in uneven growth.

Question 50

What effect does auxin have on cells in the shoots of plants?

Answer 50

Auxin stimulates cell elongation in plant shoots.

Question 51

How does auxin distribution in response to light lead to phototropism?

Answer 51

Auxin accumulation on the shaded side of a shoot causes cells on the shady side to elongate at a faster rate than cells on the light side; this leads to bending of the shoot towards the light.

Question 52

True or False? Auxin inhibits the growth of cells in plant roots.

Answer 52

True. Auxin accumulates on the lower side of plant roots, inhibiting cell growth and causing roots to bend downwards towards gravity.

Question 53

What is the endocrine system?

Answer 53

The endocrine system is composed of glands that secrete hormones directly into the bloodstream.