Transport in Animals

Question 1

Define ‘hydrophyte’

Answer 1

Plants which are adapted to survive at their optimum in water.

Question 2

What are examples of hydrophytes?

Answer 2

• Duckweed
• Water lily
• Lotus (Nelumbo)
• Rice

Question 3

What are 4 problems faced by hydrophytes?

Answer 3

1. Water contains less dissolved gases than air — but plants need Oxygen for respiration and Carbon dioxide for photosynthesis.
2. Below the water, there is less light, because light is refracted by the water molecules.
3. Water flow might disturb plants.
4. The concentration of ions in open water are lower than in soil water.

Question 4

What are 5 adaptations of hydrophytes?

Answer 4

1. Very thin/no waxy cuticle
2. Many stomata that are permanently open
3. Reduced structural support
4. Wide, flat leaves
5. Small roots

Question 5

How does being very thin with no waxy cuticle help hydrophytes?

Answer 5

• No waxy cuticle = doesn’t need to conserve water.
• Thin cuticle = more efficient gas exchange.

Question 6

How does having many stomata that are permanently open help hydrophytes?

Answer 6

Stomata can be open all the time as the plant is never dry

Question 7

How does having reduced structural support help hydrophytes?

Answer 7

• Stems can be bendy/flexible as they are not needed for support — they are supported by water. It needs to have lots of air spaces for movement of gases throughout the plant to the roots which add buoyancy, but are also a reserve of gases (O and CO).
• Very little xylem or other tissues for strengthening as it is unnecessary which means the stems are flexible and can move with the water currents without getting broken.

Question 8

How does having wide, flat leaves help hydrophytes?

Answer 8

• Increased surface area to maximise light absorption.

Question 9

How does having small roots help hydrophytes?

Answer 9

• Roots are often also reduced as their main function is anchorage.
• Root hairs which function in absorption are absent.

Question 10

Define ‘xerophyte’

Answer 10

Plants which are adapted for optimum life in very dry environments.

Question 11

Give examples of xerophytes.

Answer 11

• Cacti
• Marram grass
• Pine trees

Question 12

Describe the leaves in xerophytes.

Answer 12

• Spines like those found in some cacti (photosynthesis occurs in their stems which contains photosynthetic cells).
• Needles like those found in pine/fir trees.
• Absent e.g. some succulents.

Question 13

What are 7 adaptations of xerophytes?

Answer 13

1. Thick waxy cuticle
2. Sunken stomata
3. Reduced numbers of stomata
4. Reduced leaves
5. Hairy leaves
6. Curled leaves
7. Extensive roots

Question 14

How does having thick waxy cuticles help xerophytes?

Answer 14

• Shine of the cuticle will reflect light and heat.
• Increases the diffusion distance across which water moves therefore decreasing the rate of transpiration.
• Waxy material is also waterproof.
• E.g. holly leaves.

Question 15

How does having a sunken stomata help xerophytes?

Answer 15

• Maintains humid air around stomata.
• E.g. marram grass, cacti.

Question 16

How does having reduced numbers of stomata help xerophytes?

Answer 16

• Stomata are gaps in the surface of the leaf which allow gas exchange, but every time a stomata is opened, water will escape.
• The lower the number of stomata in a given area, the less water moves out of the leaves by transpiration.

Question 17

How does having hairy leaves help xerophytes?

Answer 17

• Trap water vapour and so reduce the water potential gradient.
• Makes the leaves lighter/shiny so reflecting more light and heat.
• Maintains humid air around stomata, reducing water potential gradient and transpiration.
• E.g. marram grass, couch grass.

Question 18

How does having curled leaves help xerophytes?

Answer 18

• Marram grass has roled leaves which trap moist air inside, reducing rate of transpiration.
• Exposes a smaller surface area of the leaf to the drying effects of the wind.

Question 19

Summarise how water moves through a plant.

Answer 19

• Enters the plant through root hairs and crosses the root hairs, the epidermis, the cortex, the endodermis, the pericycle, and into the tracheary elements (the vascular bundles where we would find xylem and phloem).
• Water is carried upwards through the xylem to the leaves.
• When water gets to the leaves, it is able to pass through the xylem out into the tissues, coating the cells, allowing them to get the water they need.
• Some of that water is lost from the leaves out through pores (stoma) between guard cells.

Question 20

What is xylem?

Answer 20

Xylem is a water transport tissue which we find throughout a plant reinforcing lignin, its dead cells, which carry water upwards through factors of adhesion and cohesion to maintain a constant flow of mass flow throughout the plant up to the leaves.

Question 21

What is stomata?

Answer 21

A group of guard cells and stoma.

Question 22

Why is floating helpful for hydrophytes?

Answer 22

• Leaves are closer to the light for photosynthesis, meaning they have direct access to the gases in the air.
• They can out-compete any plants which live lower in the water than them.
• They can move around if the water flows.

Question 23

What are adaptations of duckweed?

Answer 23

• Floats so it has access to light.
• Long roots to enable it to have a large surface area for absorption of minerals.
• No stem — it has been more successful without investing in the growth of a stem.
• They can reproduce very quickly, often covering a pond in a very short time.
• They don’t need a very thick cuticle — doesn’t need to conserve water.

Question 24

Why can adaptations help a plant?

Answer 24

It can conserve its energy —> less tissues produced —> less need for resources.

Question 25

How are water lily leaves adapted?

Answer 25

• Thin cuticle and stomata on upper surface makes gas exchange more efficient.
• The stomata can be open all the time — the plant is never dry.
• Lots of photosynthetic cells on the upper surface —> higher success in production of sucrose and other organic materials.
• Layer of buoyancy —> lots of air space which makes the leaf float (between mesophyll cells).

Question 26

How is rice adapted?

Answer 26

• Rice plants need a lot of ATP for biosynthesis so they need a lot of oxygen. In water there is less oxygen so they need to channel gas from the air down to the roots.
• The stem and root tissues have large air spaces/tubes.
• The tubes within the stem and roots are called aerenchyma —> supply oxygen rich air to the spaces and then to the root hair cells which need to carry out aerobic respiration.
• The root hair cells can then absorb minerals using active transport.

Question 27

How are pine trees adapted?

Answer 27

• Pine trees need to conserve water in winter. They have needles instead of flat open leaves.
• They have very few stomata which are in pits. This keeps air saturated with water which collects close to the stomata, reducing water potential gradient between the inside and outside of the leaf.

Question 28

Describe the epidermis of cacti.

Answer 28

• Rhipsalis dissimilis
• Crater-shaped depressions with a guard cell each at their base can be seen.
• Cross-section through the epidermis and underlying tissues.
• The guard cells are countersunk, the cuticle is thickened.

Question 29

How is marram grass adapted?

Answer 29

• Marram grass on the sand dunes have very little available water.
• Their leaves are rolled so that inside the curve their is less wind and a more humid atmosphere.
• Stomata on the inside of rolled leaf creates local humidity and decreases exposure to air currents because water vapour evaporates into air space rather than atmosphere.

Question 30

How do grooves help xerophytes?

Answer 30

• Grooved leaves allow water vapour to accumulate reducing the water potential gradient.

Question 31

How are cacti adapted?

Answer 31

• Cacti have stems that are swollen and full of water.
• Can be great source of water for animals which life in dry habitats as, when the leaf is broken, water will ooze out — so cacti have thorns which prevent animals from taking their water.

Question 32

Describe the roots of plants living in dry regions.

Answer 32

• Long tap root growing deep into the sand to get groundwater sources (e.g. Marram grass).
• Shallow roots spread over wide distances which allows them to collect lots of water very quickly when it rain in addition to the deep roots (Marram grass has a mat of shallow roots to obtain water).

Question 33

What are 2 other unique strategies xerophytes use to withstand dry conditions?

Answer 33

1. Leaf loss: To prevent water loss in extreme dry conditions, some plants will lose their leaves completely. Coupled with this, some plants will concurrent photosynthesis from stems. Others become dormant until rain arrives.
2. Avoiding drought: Some plats will survive periods of drought as storage organs, like tubers or bulbs, that will grow again when there is greater water availability.

Question 34

Describe aerenchyma in hydrophytes.

Answer 34

Specialised parenchyma in leaves, stems, and roots with thin walls and large intracellular spaces form. These make leaves and stems more buoyant and form a pathway for internal gas circulation.