Topic 2 - Plant Transport

Question 1

Why do smaller, unicellular organisms not have transport systems?

Answer 1

Smaller, unicellular organisms have no transport systems as their Surface Area : Volume (SA:V) ration is large, and due to their high SA:V ratio, diffusion is fast and efficient and can be relied on to gain nutrients and resources needed for life

Question 2

Why can large, multicellular organisms not rely on diffusion to gain resources needed for life?

Answer 2

They have a low SA:V ratio, and so are too big to rely on diffusion alone, and diffusion is slow in such low SA:V ratios and such large animals

Question 3

What are the two major tissues (tubes) in plant roots and stems that plants use to transport substances?

Answer 3

1. Xylem
2. Phloem

Question 4

What is the name of what is made up by the xylem and phloem together?

Answer 4

The vascular bundle

Question 5

What is the position of the vascular bundle in a stem?

Answer 5

A stem is circular, with small arrows (similar to a mouse cursor) arranged in a circle inside the circle. The point faces to wards the centre, and the arrows/triangles are split into two with a horizontal line in the middle, the closest half to the middle in the xylem, and the part closer to the outside circle of the stem is the phloem (Google if this doesn’t make sense)

Question 6

What is the position of the vascular bundle in a root?

Answer 6

The root is circular, and in the middle is another circle. Inside this circle is the xylem, arrange similar to a + sign. The rest of the circle is the phloem. The cortex is the area between the outside wall circle and the small inner circle containing the phloem and xylem. (Google if this doesn’t make sense)

Question 7

1. What does the xylem carry?
2. What direction(s) does the xylem transport substances

Answer 7

1. The xylem carries water and mineral ions
2. The xylem carries substances up the plant (one-way transport - from the roots to the top of the plant)

Question 8

1. What does the phloem carry?
2. What direction(s) does the phloem transport substances?

Answer 8

1. The phloem carries sucrose (sugars) and amino acids
2. The phloem carries substances both up and down the plant

Question 9

What is the process of the xylem transporting water and mineral ions called?

Answer 9

The transpiration stream

Question 10

What are 5 key structural features of the xylem?

Answer 10

1. The xylem is made of dead cells
2. There are no end walls between cells (This ensures the one way flow of water and minerals)
3. Xylem cells have no cytoplasm, and so instead have a hollow centre called a lumen
4. The walls of xylem vessels contain a woody material called lignin, which is waterproof
5. The walls are impenetrable to water (This ensures that water flows efficiently inside the tube up towards the leaves.

Question 11

What is the process of phloem transporting sucrose and amino acids called?

Answer 11

Translocation (Occurs between source and sink)

Question 12

What are 4 key structural features of the phloem?

Answer 12

1. The phloem tube consists of living cells
2. The cells have cell walls made of cellulose so they retain their cytoplasm
3. The end wall of each cell forms a sieve plate, linking each cell with small pores
4. A long sieve tube forms along the length of the phloem, which transports sucrose and amino acids up and down the plant (two-way movement)

Question 13

What is special about sieve tube cells?

Answer 13

They have no nucleus, and so are instead controlled by companion cells, which are found at the side of the tube

Question 14

What is osmosis?

Answer 14

Osmosis is the net movement of water along the concentration gradient through a semi/partially permeable membrane from an area of high concentration to an area of low concentration

Question 15

How are root hair cells adapted for absorption?

Answer 15

They are long and so have a large surface area. They also have a thin cell wall and so have a short diffusion distance

Question 16

Why do plants need to retain water?

Answer 16

To avoid wilting, and to use in photosynthesis

Question 17

Why can losing water be beneficial for plants?

Answer 17

It can cool them down (Similar to sweating)

Question 18

What is transpiration?

Answer 18

The evaporation of water from leaves through the stomata

Question 19

How can we measure the rate of transpiration?

Answer 19

Using a potometer

Question 20

What is the (small) flaw with a potometer?

Answer 20

It actually measures water uptake, which includes the replacement of water used for cell growth and photosynthesis, however 98% of water loss is through transpiration so it is fairly accurate

Question 21

1. How does temperature affect transpiration?
2. How does light affect transpiration?
3. How does wind speed affect transpiration?
4. Howe does humidity affect transpiration?

Answer 21

1. The warmer it is, the more energy particles would have, and so the particles will evaporate/transpirate quicker
2. If it is night, the guard cells will have closed the stomata, and so water will not fall out of the leaf
3. If it is windier, the water molecules outside the leaf will be blown away, which increases the concentration gradient and so osmosis will occur quicker
4. If it is more humid, there will be more water particles outside the leaf and so the concentration gradient is decreased, and so osmosis will happen slower.

Question 22

What 3 things are important when setting up a potometer?

Answer 22

1. The shoot must be cut under water to prevent air entering the xylem
2. The whole apparatus must be airtight
3. The stem will not be perfectly round, and so vaseline must be used to form a seal around the shoot where it goes into the bung

Question 23

1. How is an air bubble created?
2. How do you reset the position of the air bubble?

Answer 23

1. An air bubble is created by lifting (the measuring cylinder/object) out of the water, wiping with a tissue and then replacing in the water
2. Using the reservoir

Question 24

What are 4 reasons why transpiration is important?

Answer 24

1. The water leaving the leaf creates a suction force that brings water in through the roots to be used for photosynthesis
2. To reduce the chance of wilting and to maintain the turgidity of plant cells
3. To supply mineral ions
4. To cool the plant down/prevent overheating