R2101 2.1 & 2.3 Structure of Plant cell & Roots

Question 1

Features and functions of nucleus?

Answer 1

Controls functions of the cell and contains DNA; DNA can replicate itself for cell division

Question 2

Where does cell division and growth occur in plants?

Answer 2

Growing points or meristems

• apical meristem (tip of bud, root)
• lateral meristem = axillary bud

Question 3

How do plants increase in size?

Answer 3

1. Primary growth: meristematic tissue in the apical and lateral meristems of the stems and roots divides

2. Expansion (or elongation)

3. Differentiation (?)

Question 4

Describe cell division.

Answer 4

• duplication of the genetic material and its equal distribution to each of two ‘daughter’ cells
• usually preceded by cell growth, so that when the cell divides, the two daughter cells are essentially similar to the parent cell
• in mitosis the daughter cell ends up with exactly the same number of chromosomes as the parent cell
• takes place when an organism grows, replaces old cells or reproduces asexually

Question 5

Describe cell expansion.

Answer 5

As new cells are formed, older ones expand.

At first the cell is full of cytoplasm with the nucleus in the middle.

Several vacuoles come together to form the large, sap-filled vacuole.

Expansion takes place by uptake of water (by osmosis) into the developing vacuole.

The shape depends on how elastic the cell wall is, which is influenced by how cellulose is laid down.

Question 6

Difference between woody and herbaceous stem?

Answer 6

3 different stem structures:

• herbaceous dicot stems which have discrete vascular bundles arranged in cylinder appearing in narrow rings
• woody dicot stems which have vascular bundles in ring
• monocot stems which have scattered vascular bundles.

http://www.bio.miami.edu/dana/dox/stem.html

Question 7

Where does each of the following take place:

i) photosynthesis
ii) control of cell turgor
iii) up-take (absorption) of minerals
iv) aerobic respiration

Answer 7

i) chloroplast
ii) vacuole
iii) cell membrane
iv) mitochondrion

Question 8

Name a plant tissue where cell division takes place.

Answer 8

apical meristem

vascular cambium

Question 9

Describe the process which causes plant cells to expand.

Answer 9

Water passes into the cell by osmosis.

As water enters, turgor pressure inside the cell presses outwards against the cell membrane and stretches it and therefore expands the cell.

Question 10

Describe osmosis.

Answer 10

Diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a selectively permeable membrane

Question 11

Name the cell component that carries out the following functions:

i) limits cell expansion
ii) water storage
iii) suspends cell organelles

Answer 11

i) cell wall
ii) vacuole
iii) cytoplasm

Question 12

Functions of cell membrane?

Answer 12

Controls the movement of substances in and out of the cell.

Question 13

Functions of vacuole?

Answer 13

Controls cell turgor/stores waste products and water.

Question 14

Functions of cell wall?

Answer 14

Controls the shape of the cell/limits cell expansion

Strengthens the cell and supports the plant

Question 15

Functions of chloroplast?

Answer 15

Site of photosynthesis/site of chlorophyll synthesis

Question 16

Functions of nucleus?

Answer 16

Contains genetic information so controls cell processes

Question 17

Functions of cytoplasm?

Answer 17

A jelly-like material that contains dissolved nutrients and salts and suspends organelles. It is where many of the chemical reactions happen; its outer membrane is the cell membrane.

Question 18

Functions of cell membrane?

Answer 18

Uptake of minerals through semi-permeable membrane

Question 19

Functions of mitochondria?

Answer 19

Generates the chemical energy to power the cell’s biochemical reactions.

Chemical energy produced by the mitochondria is stored in a small molecule called adenosine triphosphate (ATP).

Play a fundamental role in cellular respiration, releasing energy for plant processes.

Question 20

What is plant tissue?

Answer 20

A collection of similar cells performing an organized function for the plant

Question 21

i) State the primary functions of the root.
ii) Describe root types.

Answer 21

i) Anchorage, water and mineral uptake (root hairs absorb water and nutrients from the soil and move them upwards to stem and leaves); store carbohydrates and water (e.g. carrot)
ii) Tap root, comes from radicle

Lateral/creeping: from the main root; do not penetrate deep into the soil; shallow and spread a long way horizontally from the base of the plant. Many trees.

Fibrous: grow from the base of the stem; close to the surface and spread horizontally; monocots

Adventitious: from stem; underground or above the ground. Can grow from any part of the plant except the radical. Usually, from intermodal, stem nodes, and leaves. Can be thick, thin, or modified according to the species. Arise under stress conditions such as waterlogging after floods.

Tuberous: very thick; store significant amounts of food to feed the whole plant. A fleshy, enlarged, and modified storage organ. Modified from the stem.

Question 22

What is the Casparian strip?

Answer 22

Casparian strip – control of water/minerals; forces them away from cell walls and through cell membrane into cytoplasm of cell and through plasmodesmata (little hole) to get into pericycle. Protects from toxins and pathogens.

Question 23

Describe the root cap

Answer 23

• Protects the root surface near to the tip where growth occurs
• A cone-shaped structure that covers the root tip
• The cells are continuously worn away by friction and are replaced by the meristem

Question 24

Describe root hairs

Answer 24

• An extension of an epidermal cell up to 4mm long
• Fragile parts of cells that grow from the main root
• They massively increase the surface area for absorption of water and minerals
• Set back from the root tip in zone of maturation

Question 25

What is the function of root hairs?

Answer 25

• Increase surface area for water absorption.
• Aid in uptake of water. Confined to the part of the epidermis behind the tip, called the piliferous layer.
• An extension of an epidermal cell up to 4mm long.

Question 26

Name 3 root adaptations.

Answer 26

• Storage/perennation –

1. Tap root – e.g. Daucus carota
2. Root tuber – e.g. Dahlia sp.

• Climbing – adventitious – e.g. Hedera helix
• Prop root/support – e.g. Zea mays

Question 27

What is a perennating organ?

Answer 27

Present in biennial and perennial plants.

A storage organ that allows the plant to survive unfavourable seasons, such as a dry season or winter.

Examples include swollen tap roots and tubers.

The plants normally die down and survive as underground perennating organs with resting buds.

Question 28

What are adventitious roots?

Answer 28

Roots which have arisen from unexpected positions, such as roots growing from a stem in Hedera helix, a climbing adaptation. They attach to other structures for support.

Question 29

What are prop roots?

Answer 29

Develop from adventitious roots.

A ring of prop roots form from the lower nodes. These are modified for aerial and extra support. Seen in Zea mays.

Question 30

What is a tuber?

Answer 30

An adapted root or stem.

Stem tubers have eyes or nodes on them that can produce new shoots.

A root tuber is a swollen root which will produces buds at the point where the tuber is attached to the stem of the plant. Asexual reproduction

Used to provide energy and nutrients for regrowth during the next growing season.

Question 31

What is a rhizome?

Answer 31

Modified, swollen stem that grows horizontally.

Like tubers, rhizomes have buds from which new plants sprout. But tubers do not grow horizontally.

Question 32

Give an example of a rhizome.

Answer 32

Japanese knotweed (Polygonum cuspidatum)

Lily-of-the-valley (Convallaria majalis)

Question 33

What is the difference difference between a tuber and a corm?

Answer 33

Buds sprout from individual hunks on tubers (“eyes” on a potato). You can’t do this with corms and bulbs.

Tubers, unlike corms, bulbs, and rhizomes, do not multiply.

Question 34

Give an example of a tuber.

Answer 34

Dahlia, anemone, cyclamen, caladium, dahlia, peony, sweet potato, and potato

Question 35

What is a bulb?

Give an example of a true bulb.

Answer 35

An underground stem with fleshy, scale-like layers surrounding a centre bud.

true bulb plants:

Daffodils (Narcissus)

Hyacinths (Hyacinthus orientalis)

Allium (Allium atropurpureum)

Tulips (Tulipa)

Question 36

Give an example of a true bulb.

Answer 36

Daffodils (Narcissus)

Hyacinths (Hyacinthus orientalis)

Allium (Allium atropurpureum)

Tulips (Tulipa)

Question 37

What is the difference between bulbs and tubers?

Answer 37

Bulbs: round; consist of one swollen stem; grow from one fixed point

Tubers: various shapes and form in a cluster; grow out of the “eyes” (e.g. Solanum tuberosum)

Question 38

What is a corm?

Answer 38

Like bulbs, they are swollen underground stems that store food for the plant during dormancy.

Unlike bulbs, corms are solid and do not have scales or fleshy leaves.

Question 39

What are tuberous roots?

Answer 39

Swollen roots near the base of the original plant

Just as with swollen stems, these swollen roots store extra food for the plant, but they do not propagate the plant. e.g. tuberous begonias

Each tuberous root has the capability of producing a new plant, but usually the tuberous roots grow in a tangled mass of roots and stems. Instead of starting from a single root piece, plants such as dahlias, daylilies and peonies are divided so that several swollen roots are still attached to a portion of the old stem.

Question 40

What is a rhizome?

Give an example of a rhizome.

Answer 40

Modified, swollen stem that grows horizontally.

Like tubers, rhizomes have buds from which new plants sprout. But tubers do not grow horizontally.

Japanese knotweed (Polygonum cuspidatum)

Lily-of-the-valley (Convallaria majalis)

Question 41

What is the difference difference between a tuber and a corm?

Give an example of a tuber.

Answer 41

Buds sprout from individual hunks on tubers (“eyes” on a potato). You can’t do this with corms and bulbs.

Tubers, unlike corms, bulbs, and rhizomes, do not multiply.

Dahlia, anemone, cyclamen, caladium, dahlia, peony, sweet potato, and potato