R2101 2.3 Describe the structure and state the functions of roots

Question 1

Primary function of roots

Answer 1

1. Anchor the plant
2. Takes up water from the soil
3. Takes up nutrients from the soil
4. Can be modified to allow the plant to survive winter
5. Can be modified to help the plant spread

Question 2

What is a tap root? (4)

Answer 2

1, One primary or main root that develops from the root initial of radical
2. Has smaller secondary roots - lateral roota
3. Grow deeply into the soil to draw up water
4. Mostly dicots e.g. carrot

Question 3

What are fibrous roots? (5)

Answer 3

1. There is no tap root
2. Roots start at the base of the stem and are mutlibranched
3. They occupy a large area in upper top soil and help prevent erosion
4. They reliance of surface water means they are the first plants to show signs of water shortage
5. Mostly monocots e.g. grasses

Question 4

What are adventitious roots? (3)

Answer 4

1. Do not derive from the radicle of the plant embyro
2. Grow in unusual places such as stem
3. Most fibrous root systems are adventitious roots

Question 5

Where does a tap root originate?

Answer 5

The radicle of the embryo

Question 6

Where do fibrous roots originate?

Answer 6

The base of the stem

Question 7

Where do adventitous roots originate?

Answer 7

Unusual places. NOT the radicle of the embyro

Question 8

Difference between a monocotyledon root v dicotyledon root

Answer 8

Moncot - Xylem and phloem cells are arranged around in a circle around a pith or centre

Dicot - Xylem cells form a central hub with lobes and phloem cells fill in the spaces between the lobes

Question 9

Root Cap function (3)

Answer 9

1. Layer of cells that protect the root tip
2. Exudes a gel enabling root tip to grow through the soil more easily.
3. Cells constantly being replaced

Question 10

Root Tip function (1)

Answer 10

1. This is the apical meristem where cell division takes place.

Question 11

Root hair function (4)

Answer 11

1. Elongated epidermal cells that occur in a zone just behind the root tip
2. They greatly increase the surface area of roots to bring them into contact with more water and nutrients
3. Usually live 1 or 2 days
4. Easily damaged when a plant is transplanted

Question 12

Zone of elongation (4)

Answer 12

1. Just behind the meristem
2. Cell expansion occurs here
3. Caused by turgor pressure with cell pushing outward on cell membrane
4. When the cell has differentiated to its final form the cell wall loses elasticity and can expand no further.

Question 13

Zone of cell division (1)

Answer 13

1. New cells form in the apical meristem by cell division

Question 14

How do roots grow in length and size? (2)

Answer 14

1. Length by cell division (zone of cell division)
2. Size by cell expansion (zone of elongation)

Question 15

Zone of differentiation (4)

Answer 15

1. Cells adopt their final roles
2. Cell walls become rigid
3. Connections (plasmodesmata) between cells form
4. This where the epidermis, cortex, vascular tissues and pith become distinct

Question 16

What is epidermis and function in roots? (2)

Answer 16

1. Outer layer of cells with a protective and absorptive function
2. Unlike stem it lacks cuticle as reducing water loss is not necessary in a root

Question 17

Cortex and function (3)

Answer 17

1. Thick layer of cells that produces energy by respiration or root growth
2. Used to store starch when root is an over wintering organ
3. Water can pass through the cells of the cortex

Question 18

Endodermis and function (1)

Answer 18

1. Inner ring of cells that control movement of water from the cortex to xylem and phloem

Question 19

Pericycle and function (2)

Answer 19

1. Has cells which are able to divide and produce lateral roots. Made of parenchyma or sclerenchyma cells. Strengthens roots and protects vascular bundles.
2. As the roots age they become thickened with waxy substances which restrict the uptake of water

Question 20

Phloem function (1)

Answer 20

1. Carries food from leaves to all other parts of the plant

Question 21

Xylem function (1)

Answer 21

1. Carries water and nutrients from the roots to other parts of the plant.
2. In dicots a transverse section of the root will show this tissue as a star with several arms.

Question 22

Vascular cambium function (1)

Answer 22

1. Thin cell layer between xylem and phloem that manufactures new cells from each

Question 23

What is the stele? (1)

Answer 23

1. Central regions separated by the cortex by the endodermis
2. The stele (or vascular cylinder) is in the central region of the root, where the xylem and phloem develop.
3. Outside the stele lies the endodermis,

Question 24

What is in the stele? (4)

Answer 24

1. Pericycle
2. Xylem
3. Phloem
4. Vascular cambium

Question 25

What is perennation?

Answer 25

The storing of food in the form of starch over the winter, giving plants a head start when growth resumes in the spring
e.g. Daucus carota (carrot)

Question 26

What are butress roots? (4)

Answer 26

1. Adapted adventitious roots
2. Support for tropical plants
3. Plank like out growths of the stem supporting tall forest trees on shallow soils
4. e.g. Ficus macrophylla

Question 27

What are stilt roots? (3)

Answer 27

1. Adapted adventitious roots
2. Roots dropping down from branches to the ground
   3 e.g. Mangroves

Question 28

What are prop roots? (3)

Answer 28

1. Adapted adventitious roots
2. At the base of tall stems, just above the surface of the ground to support the stem
3. e.g. Zea mays (sweet corn)

Question 29

What are pneumatophores? (2)

Answer 29

1. Breathing roots adapted for waterlogged soils
2. Covered in many lenticels that act as snorkels to obtain oxygen for respiration

Question 30

What are climbing roots? (4)

Answer 30

1. Adapted adventitious roots
2. Help plants grow towards the light, clinging on to walls and fences.
3. Raise flowers up for better pollination opportunities
4. e.g. Hedera helix (ivy)

Question 31

What are aerial roots? (3)

Answer 31

1. Adapted adventitious roots
2. Grow high into the canopy of their native tropical forests to reach light and take up extra moisture from the air
3. e.g. Monstera deliciosa

Question 32

What are haustorial roots? (2)

Answer 32

1. Roots that penetrate into the vascular system of the host to tap into water and sugars
2. e.g. Viscum album (mistletoe)

Question 33

What are velamen roots? (4)

Answer 33

1. A form of aerial roots
2. Absorb water from the air and reduce water from the root tissue and it seems it is able to take up nutrients dissolved in moisture in the air.
3. Unsually these roots are green and can photosynthesize
4. e.g. Epiphytic Orchids

Question 34

What are root tubers? (4)

Answer 34

1. Develop near the base of a plant
2. Distinguished from stem tubers in having lateral roots and no nodes
3. e.g. Ipomoea batatas
4. Perennating organ

Question 35

Examples of Perennating organs (2)

Answer 35

1. Root tubers e.g. Ipomoea batatas
2. Swollen taproot e.g. Daucus carota

Question 36

Root modifications for survival (5)

Answer 36

1. Help the plant reach light and photosynthesise e.g. climbing roots
2. Spread widely by forming new roots from plant segments e.g. adventitous roots
3. To store large amounts of food, as starch, for over-winer e.g. perennating organ
4. Take moisture out of humid air e.g aerial roots, velamen roots
5. To provide support above ground for extra stability - butressing e.g. butress roots, stilt roots, prop roots