Chapter 8 : Transport In Plants

Question 1

Name the 2 types of vascular tissue in a plant

Answer 1

Phloem
Xylem vessels

Question 2

Functions of the xylem (2)

Answer 2

Conducts water and mineral salts from the root of the plant to the stem and leaves ( 1 direction)
Provides structural support to the plant

Question 3

What is the structure of the xylem

Answer 3

• many dead cells fused together at the ends to form a long hollow tube
• continuous empty lumen with no cross walls or protoplasm
• lignin deposits in the inner wall of the xylem

Question 4

How is the xylem adapted for its function?

Answer 4

Empty lumen without cross wall or protoplasm ( allows water to move in easily )
Walls are lignified to prevent the collapse of vessels

Question 5

Function of phloem ?

Answer 5

Translocate manufactured food from leaves to other parts of the plant (bi-directional)

Question 6

What does translocation mean

Answer 6

Transport of manufactured food substances from leaves to other parts of the plant. It is a bi-directional process.

Question 7

What does conduction mean ?

Answer 7

Transport of water and dissolved mineral salts from the roots to the stem and leaves

Question 8

What is the structure of the phloem

Answer 8

• sieve tube cells (elongated cells that lack nuclei and have thin layers of cytoplasm) joined together To form a sieve tube element with sieve plates in between
• sieve tube cells are accompanied by a companion cell which contains numerous mitochondria

Question 9

How is phloem adapted for its function (4)

Answer 9

1. Sieve tube elements have little protoplasm - reduces resistance to the flow of substances within the phloem
2. Pores within the sieve plate allow rapid flow of manufactured food substances
3. Companion cells have numerous mitochondria to provide energy to the sieve tube cell for loading of sucrose and amino acids
4. Presence of companion cell for every single sieve tube cell

Question 10

Describe the process of translocation

Answer 10

1. Sucrose is loaded into the sieve tube at the source through active transport. Water potential at that sieve tube cell decreases.
2. This causes water to flow into the cell from the xylem vessel through osmosis. Uptake of water causes water at the source to be high in pressure
3. Phloem sap would then flow to a region with lower pressure ( the sink cell )
4. The pressure is then diminished when the sink cell takes in the sucrose and converts it into insoluble starch. Starch, being insoluble, will not affect the water potential
5. Xylem then recycles the water by carrying it from the sink back to the source

Question 11

Differences between xylem and phloem

Answer 11

1. Xylem is made of dead cells while phloem consists of living cells
2. Transport in xylem is uni-directional while transport in phloem is bi-directional
3. Substances in xylem transported by passive transport, substances in phloem transported by active and passive transport

Question 12

Similarities and Difference between pith and cortex

Answer 12

Pith is the tissue internal to vascular tissue
Cortex is the tissue external to vascular tissue

Both are storage tissues

Question 13

What is the tissue between the xylem and phloem and what is its function ?

Answer 13

Cambium. Cambium cells can divide and differentiate into either xylem or phloem cells, causing a thickening of the stem

Question 14

The stem is covered by a layer of cells called the ___________ . The __________ cells are protected by a waxy, waterproof _________ which reduces evaporation of water from the stem

Answer 14

Epidermis, epidermal, cuticle

Question 15

What is the sclerenchyma and what is its function ?

Answer 15

It is a plant tissue found outside of the phloem. Provides mechanical stiffness and strength to the stem of plant

Question 16

Name the parts of the stem, starting from the innermost part.

Answer 16

1. Pith
2. Xylem
3. Cambium
4. Phloem
5. Sclerenchyma
6. Cortex
7. Epidermis
8. Cuticle

Question 17

How do the xylem and phloem in a root differ from in a stem

Answer 17

In the stem, xylem and phloem are bundled together whereas in the root, the xylem and phloem alternate with each other. (Large central xylem like a start with phloem in btw each tip)

Question 18

The root does not have a pith but has a ______ . The innermost layer of the ______ is called the endodermis

Answer 18

Cortex, cortex

Question 19

What is the difference between the epidermis in the stem and piliferous layer in the roots

Answer 19

Each epidermal cell in the root has a tubular outgrowth known as root hair. The root hair increases the SA:V of the cell

Question 20

Describe how water enters a plant (6)

Answer 20

1. Root hairs grow in btw soil particles and are in close contact.
2. Each soil particle has a thin film of moisture surrounding it, containing mineral salts.
   3.The water potential of the cell sap is lower in than the soil solution.
3. Hence water enters the root through osmosis, increasing the water potential of the cell sap.
4. The water then passes through osmosis into neighbouring cells with lower water potential, moving inwards.
5. Water is then conducted upwards by the xylem

Question 21

Adaptations of root hair cell ?

Answer 21

1. Long and narrow ( Higher SA:V )
2. Numerous mitochondria ( aerobic respiration to generate energy for active transport of mineral ions )
3. Prescience of cell membrane ( prevents leakage of cell sap and allows water to enter by osmosis )

Question 22

How are mineral salts absorbed into the cell ?

Answer 22

1. Active transport —> when conc. In cell sap > conc in soil solution
2. Diffusion —> when conc. In cell sap< conc in soil solution

Question 23

Why is water and mineral ion absorption decreases in water logged soil ?

Answer 23

Water logged —> Low conc. Of O2
1. Decr rate of respiration by root hair cells
2. Decr rate of absorption of mineral salts by diffusion and active transport
3. Decr rate of osmosis

Question 24

3 forces that aid in the upward motion of water

Answer 24

1. Root pressure
2. Capillary action
3. Transpirational pull

Question 25

What is root pressure ?

Answer 25

Root pressure is the pressure resulting from constant entry of water into the roots

Question 26

What is capillary action?

Answer 26

Tendency of water to move up in very narrow tubes. Depends on the forces of cohesion and adhesion of water.

Question 27

What is transpiration pull ?

Answer 27

Loss of water vapour, especially through the aerial parts of a plant, stomata of the leaves, causes suction pull of water up the xylem .

Question 28

Describe movement of water through a leaf (7)

Answer 28

1. Water moves our the mesophyll cells and form a thin film of moisture around the cells
2. Water then evaporates to form water vapour in the air spaces, accumulating in air spaces near the stomata
   3.Water vapour diffuses into the surroundings
3. Water moves out of the cell to replaces film of moisture which has evaporated
4. Mesophyll cells absorb water via osmosis from cells further in the leaf.
5. Those cells then absorb water from the xylem vessels
6. This results in a suction force which pulls water upwards

Question 29

State the factors affecting rate of transpiration

Answer 29

1. Humidity of air
2. Wind or air movement
3. Presence of light
4. Temperature

Question 30

Why is transpiration important (4)

Answer 30

1. Moves essential mineral salts and water up the plant
2. Provides water required for photosynthesis
3. Turgidity of cells remains
4. Evaporation of water helps to cool the plant

Question 31

Excessive transpiration can lead to wilting. What are advantages and disadvantages of wilting

Answer 31

Advantages
1. Reduces rate of transpiration
2. Reduces water loss

Disadvantages
1. Stoma close, Decr rate of CO2 intake and rate of photosynthesis
2. Leaves droop and absorption of sunlight decreases, rate of photosynthesis decreases

Question 32

What are xerophytes?

Answer 32

Xerophytes are plants adapted to live in dry habitats

Question 33

What is used to measure rate of transpiration

Answer 33

Potometer