plants

Question 1

Need for transport systems.

Answer 1

• Plants need substances like water, minerals and sugars to live. Also need to get rid of waste materials.
• Multicellular, so have a small surface area to volume ratio. They’re also relatively big with a relatively high metabolic rate.
• Exchanging substances by direct diffusion from outer surface to the cells would be too slow to meet the metabolic needs, due to large transport distance.

Question 2

What is mass transport?

Answer 2

This is the bulk movement of materials. Involves some source of force.

Question 3

What does mass transport system help to do?

Answer 3

• Bring substances quickly from exchange site and to another.
• Maintain the diffusion gradients at exchange sites and between cells and their fluid surroundings.
• Ensure effective cell activity by keeping the immediate fluid environment of cells and within a suitable metabolic range.

Question 4

What are the two mass transport systems?

Answer 4

• The xylem transports water and minerals ions.
• The phloem transports sucrose and other nutrients.

Question 5

what are the key features of xylem?

Answer 5

• Dead cells have been fused to form hallow vessels, which are strengthened by lignin.
• Pits in the xylem wall enable water to move out into adjacent xylem vessels or other cells.
• Xylem fibres add strength, and xylem parenchyma cells store food.

Question 6

Functions of xylem.

Answer 6

• Transport of water and mineral ions up a plant.
• The tissue also provides structural support for the plant.

Question 7

Key features of phloem.

Answer 7

• Sieve tube elements are living cell joined end- to- end, forming a tube with an internal pores. (sieve plates)
• Companion cells carry out all the metabolic functions of the phloem tissue. Materials pass into sieve tubes via plasmodesmata.

Question 8

Function of phloem.

Answer 8

Transport of solutes (e.g sugars and amino acids)

Question 9

What type of microscope can observe xylems?

Answer 9

Light microscope.

Question 10

What is the transpiration pull?

Answer 10

When water is pulled up through xylem vessels to replace the water loss through transpiration.

Question 11

What is the transpiration stream?

Answer 11

An unbroken chain of water molecules to be pulled up the xylem vessels.

Question 12

What is capillary action in xylem?

Answer 12

Water molecules adhere to the sides of xylem vessels, which helps move the transpiration stream up narrow vessels.

Question 13

What is evidence for the cohesion-tension theory?

Answer 13

• Trees become narrower when they transpire; this can be explained by the increased tension in xylem vessels during high rates of transpiration.
• Air is sucked up when a stem is cut.
• Water is no longer moved up a broken stem because the air that is pulled in breaks the transpiration stream.

Question 14

What does the opening of the stomata allow?

Answer 14

• Allow exchange of CO2 and O2 but also leads to transpiration and the loss of water.

Question 15

What controls the opening and closing of stomata?

Answer 15

Guard cells.

Question 16

How does light intensity affect transpiration and what increases transpiration rate?

Answer 16

• Stomata open in the light.
• Higher light intensity increases transpiration rate.

Question 17

How does temperature affect transpiration?

Answer 17

• Changes the kinetic energy of molecules, higher temperature increases transpiration rate.

Question 18

How does humidity affect transpiration?

Answer 18

• Affects the water potential gradient between leaf and air.
• Lower humidity increases transpiration rate.

Question 19

How does air movement affect transpiration?

Answer 19

• Affects how quickly moist air is removed.
• more air movement increases transpiration rate.

Question 20

How does number of leaves affect transpiration?

Answer 20

• Affects the surface area available for loss of water vapour.
• More leaves increases transpiration rate.

Question 21

How does number of stomata affect transpiration?

Answer 21

• Alters how much water is able to diffuse from the leaves.
• More stomata increases transpiration rate.

Question 22

How does thickness of cuticle affect transpiration?

Answer 22

• Waxy cuticles reduce the water loss.
• Thin cuticles increase transpiration rate.

Question 23

What does a potometer measure?

Answer 23

Measures rate of transpiration.

Question 24

What must you control when using a potemeter?

Answer 24

• Shoot must be cut under water and placed into potemeter under water so that air does not get into the xylem vessel.

Question 25

How can you view the change in rate in transpiration in a potemeter?

Answer 25

• By changing a factor such as the light level or temperature and measuring how fast a bubble moves along a glass tube.

Question 26

What is the volume of a cylinder?

Answer 26

pi x r^2 x l