Adaptation For Transport In Plants

Question 1

Describe structure of roots and how this is beneficial to the plant

Answer 1

• xylem is central and star shaped
• phloem between groups of xylem cells
• resists vertical stresses and anchors plant in soil

Question 2

Describe the structure of stems and how this is beneficial to the plant

Answer 2

• vascular bundles are in a ring at the periphery: xylem towards the centre, phloem towards the outside
• gives flexible support and resists bending

Question 3

Describe the structure of leaves and how this is beneficial for the plant

Answer 3

• vascular tissue in the midrib and in a network of veins

- flexible strength and resistance to tearing

Question 4

What are the main cell types in xylem?

Answer 4

Vessels and tracheids

Question 5

What plant do tracheids occur?

Answer 5

Ferns, conifers and angiosperms

Question 6

Why do mosses not grow as tall as other plants?

Answer 6

No water conducting tissue

Poorer at transporting water

Question 7

What are the only plants that vessels occur in?

Answer 7

Angiosperms

Question 8

What are the functions of xylem?

Answer 8

1. Transport of water and dissolved minerals

2. Providing mechanical strength and support

Question 9

How is water taken up by roots?

Answer 9

• soil water contains dilute solution of mineral salts- high water potential
• vacuole and cytoplasm of root hair cell have concentrated solution of diluted- more negative water potential
• water passes into root hair cell by osmosis

Question 10

What is the apoplast pathway?

Answer 10

Water moves in the cell walls

Cellulose fibres in the cell wall are separated by spaces through which the water moves.

Question 11

What is the symplast pathway?

Answer 11

Water moves through the cytoplasm and plasmodesmata

Question 12

What is the plasmodesmata?

Answer 12

Strands of cytoplasm through pits in the cell wall joining adjacent cells.

Question 13

What is the vacuolar pathway?

Answer 13

Water moves from vacuole to vacuole

Question 14

What is transpiration?

Answer 14

The evaporation of water vapour from the leaves or other above ground parts of the plant, out through stomata into the atmosphere.

Question 15

What are the genetic factors affecting the rate of transpiration?

Answer 15

Number, distribution and size of stomata.

Question 16

What are the environmental factors affecting the rate of transpiration?

Answer 16

Temperature
Humidity
Air movement
Light intensity

Question 17

How does temperature affect transpiration rate?

Answer 17

Increase in temperature increases kinetic energy
Water diffuses away from leaf quicker
Reduces water potential of atmosphere around the leaf

Question 18

How does humidity affect rate of transpiration?

Answer 18

Air inside leaf is saturated with water vapour- relative humidity is 100%
Water potential gradient between leaf and atmosphere
Stomata open- water diffuses out of leaf

Question 19

How does air movement affect rate of transpiration?

Answer 19

Blows away layer of humid air at the leaf surface

Water potential gradient increases- water vapour diffuses out quicker

Question 20

How does light intensity affect the rate of transpiration?

Answer 20

Stomata open wider as light intensity increases

Question 21

How do MESOPHYTES ( plants living in conditions of adequate water supplies) survive in times when water is not available?

Answer 21

• shed leaves ( do not loose water through transpiration)
• aerial parts die off so they are not exposed to cold weather
• dormant seeds over winter- low metabolic rate

Question 22

Marram grass is a XEROPHYTE. How is it adapted to live in low water availability?

Answer 22

• rolled leaves: reduces leaf area exposed - reduces transpiration
• sunken stomata- humid air is trapped in pit, reduces water potential gradient
• hairs- trap water vapour- reduce gradient
• thick waxy cuticle- waterproof- reduces water loss

Question 23

How are HYDROPHYTES ( plants that grow in water) adapted?

Answer 23

• water is supportive medium- little or no lignified tissues
• surrounded by water- transport not needed- xylem poorly developed
• leaves no cuticle- don’t need to prevent water loss
• stomata on upper surface of floating leaves, lower surface is in water
• stems and leaves have large air spaces- reservoir for o2 and co2- provide buoyancy

Question 24

What is translocation?

Answer 24

The active movement of the soluble products of photosynthesis, such as sucrose and amino acids, through phloem, from sources to sinks.

Question 25

What experimental techniques have been used to show transport occurs in the phloem?

Answer 25

• ringing experiments
• radioactive tracers and autoradiography
• aphid experiments
• aphids and radioactive tracers

Question 26

What is the mass flow hypothesis theory of translocation?

Answer 26

Passive mass flow of sugars from phloem of the leaf, where there is the highest concentration( the source), to other areas, such as growing tissues, where there is a lower concentration ( the sink).

Question 27

What does mass flow theory not explain?

Answer 27

• rate of transport is a lot faster than if substances were moving by diffusion
• does not take into account sieve plates and companion cells
• sucrose + amino acids move at different rates and different directions
• phloem has high oxygen consumption

Question 28

What are the other theories of translocation?

Answer 28

• active process
• protein filaments
• cytoplasmic streaming