9. Plant Biology

Question 1

Define photosynthesis.

Answer 1

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water.

Question 2

What does photosynthesis require?

Answer 2

• Carbon dioxide and Water to produce carbohydrates and oxygen
• Oxygen for respiration

Question 3

What are stoma?

Answer 3

Stomata are tiny pores on leaves, usually on the underside.

Question 4

What is the function of guard cells?

Answer 4

Two guard cells surround the stoma and they control where it is open or closed and control gas exchange

Question 5

What is transpiration?

Answer 5

Transpiration is the take up of water by roots and carried through the plant to leaves for release of water vapor.

Question 6

How does transpiration occur?

Answer 6

• stomata opens up
• gas exchange occurs; oxygen desorbed carbon dio absorbed
• Due to a concentration gradient between the leaf and the atmosphere, some water diffuses out
  This causes transpiration.

Question 7

Why is transpiration essential for plants?

Answer 7

• provide raw materials for photosynthesis
• cool the leaves
• transport the minerals to leaves for use in synthesis of important molecules

Question 8

What happens if the plant does not replace the water lost during transpiration?

Answer 8

The plant will wilt and will not be able to photosynthesize efficiently

Question 9

What is the transpiration pull? And what happens during transpiration pull?

Answer 9

Transpiration pull: loss of water vapor through the stomata helps to pull the water from roots all the way up to leaves

Due to the cohesive property of water, the water is pulled upwards. Water absorbed through routes via osmosis
Higher concentration of solutes than outside
Water moves along concentration gradient

Question 10

Explain the structure and function of xylem tubes.

Answer 10

Xylem transports water from the roots to all other parts of the plant.

• The xylem tubes are long continuous tubes that run from the roots through the stems of plants.
• Walls: thickened with lignin ( a woody tissue)

Question 11

What are lignins?

Answer 11

It is a woody tissue that prevents the walls of the xylem from collapsing under pressure and adds strength to the woody material of older plants.

Question 12

What are primary xylem vessels?

Answer 12

Primary xylem vessles are the first xylem that forms from the root or shoot tip and their walls contain very little lignin in the form of annular and spiral thickening

Question 13

Why are lignin bound to break?

Answer 13

Due to the atmospheric pressure being higher than the pressure within.

Question 14

What happens once the xylem is matured?

Answer 14

• They lose their cytoplasmic content
• Converted to hollow tubes that transport water within the plant
• Flow of water is driven by passive forces

Question 15

Explain the process of transpiration.

Answer 15

• The adhesive properties of water, together with evaporation, creates tension forces in leaf cell walls that generate the transpiration pull
  This causes the upward movement of water inside the xylem vessels to the leaves to replenish the water lost through transpiration.

Question 16

What are the two forces?

Answer 16

Cohesion: water molecules are polar and stick to each other which helps water move up long distances

Adhesion: interaction between water and the wall of the xylem vessel
These forces creates a continuous stream of water through the plant

Question 17

How is lignin used for structural under tension?

Answer 17

The long continuous tubes are lignified

The lignin makes the walls of xylem which prevents the tubes from collapsing

Question 18

Explain how active uptake of mineral ions in the roots causes absorption of water by osmosis

Answer 18

Water and minerals are taken up by roots, tiny extensions on specialised root cells called root hairs take up water through osmosis. This creates a concentration gradient inside the roots and causes water to diffuse into the roots through osmosis. The concentrations are created through active transport.

Question 19

What are the two ways of water movement to the xylem?

Answer 19

Through the apoplast: water moves through the cell walls of the epidermal cells of the root.

Through the symplast: water moves through the cytoplasm of epidermal cells of the root

Question 20

What is the casparian strip?

Answer 20

It is a band of suberin, a waxy substance that is impermeable to water.

Question 21

Where is the casparian strip found?

Answer 21

Found in the cell walls of the endodermis of plant roots.

Question 22

How does water flow from the endodermis and onwards?

Answer 22

Water flows through the symplast pathways to reach the xylem vessels.

Question 23

How are minerals transported in plants?

Answer 23

• by active transport
• Protein pumps in the plasma membrane of the root hair cells actively pump minerals into the cytoplasm
• Minerals are transported while dissolve in water to the xylem vessels

Question 24

Define Xerophytes and Halophytes.

Answer 24

Xerophytes: plants that are adapted to thrive under dry conditions eg. cacti

Halophytes: plants that are adapted to living near the sea and have evolved mechanisms to cope with high levels of salt

Question 25

What are adaptations of xerophytes?

Answer 25

- reduced leaf size - succulents store more water - stomata mostly on stem - stomata open up at night - leaf coated with waxy cuticles - leaves rolled up to increase humidity around stomata - extensive shallow network of roots to absorb more water

Question 26

What are the adaptations of Halophytes?

Answer 26

- reduced leaf sizes - Water storage structures develop in the leaves - Thick cuticle and thick epidermis - Stomata sunk into pits - Some plants have -structures to remove salt build-up - Root cells pump excess sodium and chloride ions out into the surrounding soil or water

Question 27

What is the crassulacean acid metabolism?

Answer 27

To help with helping the plant not run out of carbon dioxide overnight when the stomata opens Night: Carbon dioxide is absorbed and converted into malic acid Day: Carbon dioxide is released and used for carbon fixation in the light-independent reactions.

Question 28

How can rate of transpiration be determined?

Answer 28

By measuring the amount of water lost from a plant per unit time.

Question 29

What are the 4 internal factors that affect the rate of transpiration?

Answer 29

- Root to shoot ratio - Surface area of leaves - Number of stomata - Structure of leaf

Question 30

What are the 4 external factors that affect the rate of transpiration?

Answer 30

``` Light Wind Temperature Humidity Water supply ```

Question 31

How does light effect plant transpiration?

Answer 31

Increased light intensity = increased rate of transpiration due to stomata opening and mroe water vapor escaping

Question 32

How does wind effect plant transpiration?

Answer 32

Increased wind velocity = increased rate of transpiration due to humid air carried away faster and replaced by drier air. This increases the rate of transpiration due to steep diffusion gradient of water vapor between air spaces in leaves and environment.

Question 33

What happens if there is no wind?

Answer 33

There is more humidity in air so it reduces the water vapor to the surrounding air and reduces the rate. But if there is a high velocity of wind, reduced rate because stomata close up.

Question 34

How does temperature effect plant transpiration?

Answer 34

Increased temperature = increased rate of transpiration Higher temperature = provides more energy for evaporation of water from cell surfaces and decreases the humidity of the external temperature Really high temp = stomata close and reduced rate

Question 35

How does temperature effect plant transpiration?

Answer 35

Higher humidity = higher rate of transpiration The gradient for diffusion of water vapor from stomata is not steep.

Question 36

How does water affect plant transpiration?

Answer 36

Decreased water in soil = decreased rate of transpiration If the roots cant keep up with the rate of transpiration, stomata close, leaf cells lose their turgidity and this reduces the rate.

Question 37

What are sieve plates and sieve elements?

Answer 37

Sieve plates: perforated end walls Sieve elements: the elongated living cells that form the phloem tissue Connected end to end to form a sieve tube

Question 38

What are sources and sinks?

Answer 38

Sources: photosynthesising tissues and some plant organs that export sugars to other parts of the plant Acquire substances such as organic substances in leaves Sinks: plant organs that cannot produce sugars but need them for respiration or storage Lack of the substances and need some of them through translocation

Question 39

Steps of translocation:

Answer 39

EWWW

Question 40

What is the function of phloem tubes?

Answer 40

- transports sap from sources to sinks Sap is the mixture of water, carbohydrates, minerals, amino acids and plant hormones - Ensuring all parts of the plant that performs the functions of life

Question 41

What type of process does the transport of sap from source to sink require?

Answer 41

Active transport.

Question 42

What are companion cells?

Answer 42

They perform many of the genetic and metabolic functions of the sieve elements or sieve tube cells. So that the sieve tube cell can maintain the membrane structure necessary for the high solute concentrations

Question 43

Explain how high concentrations of solutes in the phloem at the source lead to water uptake by osmosis.

Answer 43

When solutes are pooled at the source the solution becomes hypertonic in that area. Through osmosis water comes in to maintain equilibrium and as water comes in it pushes the solutes in the phloem away from the source.

Question 44

Compare the phloem and xylem tubes.

Answer 44

Phloem: - living cells - transport sugars, hormones, proteins - has companion cells - sieve tubes have sieve plates that control sap flow Xylem: - dead cells - transport water, minerals - lignin - continuous hollow tube

Question 45

Explain the dicot stem.

Answer 45

Ground tissue is differentiated into different layers such as the cortex and the pith Vascular bundles are arranged in a ring towards near the edge of the stem

Question 46

Explain the monocot root.

Answer 46

Monocot root: The ground tissue is not differentiated into different layers of tissue Vascular bundles are scattered randomly in the ground tissue

Question 47

Define meristems and state the function.

Answer 47

Meristems: the tissue in most plants containing undifferentiated cells (meristematic cells)and found in zones of the plant where growth can take place. Meristems produce continuous cell production.

Question 48

What are the two main areas where growth can occur?

Answer 48

Root tip and shoot tip. | These are called apical meristems.

Question 49

What happens to new cells when meristems produce continuous cells?

Answer 49

The new cells are immediately pushed away from the meristematic zone then towards the zone of elongation and then to the zone of differentiation

Question 50

Why does plants grow continuously?

Answer 50

Due to the continuous production of new cells by the undifferentiated cells in meristems.

Question 51

What are plant hormones?

Answer 51

They are small organic molecules that act as chemical messengers.

Question 52

State one difference and similarity of animal and plant hormones.

Answer 52

Similarity: They are effective at low concentrations Difference: Action can be restricted by the transport system as their site of production and site of action can differ

Question 53

State the function of IAA.

Answer 53

IAA inhibits the growth of axillary side buds causing the plant to grow vertically upwards to trap more light for photosynthesis. This is known as apical dominance

Question 54

What is apical dominance?

Answer 54

Apical dominance: the inhibition of the growth of axillary side buds so that the plant can grow vertically upwards to trap more light for photosynthesis

Question 55

What is cytokinin and what does it do?

Answer 55

Plant hormone produced in the root of a plant that promotes the growth of axillary buds

Question 56

Explain how plant shoots respond to the environment by tropisms, phototropism and geotropism.

Answer 56

Both can be positive, which is growth towards the stimulus or negative, which is growth away from the stimulus. Shoots show positive phototropism and negative gravitropism. Grow directly towards the source of light and away from gravity Shoots receive maximum light for photosynthesis

Question 57

What makes shoots and roots respond in the way they do to light and gravity?

Answer 57

In both cases, the unequal distribution of auxin has been found to be the cause.

Question 58

How do shoots grow?

Answer 58

Shoots: Auxin produced at the shoot tip diffuses towards the zone of elongation and is evenly redistributed Cells grow at the same rate causing the shoot to extend vertically upwards More light = grows faster because more auxin concentration Thus the shoot bend towards the light source

Question 59

How do roots grow?

Answer 59

Roots: Plant positioned horizontally Light from above and gravity from below will cause accumulation of auxin on the below. This causes inhibition on below, and elongation on upper This causes the bending of the root towards gravity

Question 60

What is phototropism?

Answer 60

Regulated by proteins called phototropins | Phototropins regulate the transcription of genes that may play a role in the transport of auxin

Question 61

Why do plants produce the two proteins?

Answer 61

To support the passing in and out of the layers and moving vertically down the stem

Question 62

Briefly explain about the auxin influx proteins.

Answer 62

- Found at the top part of the cell | - To take in auxin into the stem

Question 63

Briefly explain about the auxin effux proteins.

Answer 63

- Found at the basal membrane (base) | - To remove auxin

Question 64

Explain the process of cell to cell movement of auxin.

Answer 64

1. Under normal light conditions, auxin pumped into a cell by mersitem, exits the cell 2. The removed auxin re-pumped into cell below 3. Auxin moves down the stem with the help of auxin efflux pumps that creates concentration gradients of auxin in plant tissue : highest concentration is at the meristem and the base of the plant

Question 65

What happens to the plant when light just shines at one side?

Answer 65

Auxin efflux proteins redistribute the auxin laterally towards the shaded part of the cell So any auxin entering the cell from the apex is pumped out laterally towards the neighbouring cell, which responds by elongating Thus, causing the bending of the shoot and grow towards the light

Question 66

How does auxin influence cell growth rates by changing the pattern of gene expression

Answer 66

- Changing the pattern of gene expression - Enhances the expression of genes that code for wall loosening enzymes and expansin proteins - They go into the cell wall and are activated in the presence of hydrogen ions to break certain bonds to loosen the wall - This causes the cell to expand

Question 67

How does micropropagation work?

Answer 67

Involves the use of tissue culture techniques where plants are grown under controlled conditions from meristematic tissue or somatic cells on nutrient media in vitro

Question 68

How is micropagation used?

Answer 68

- replication of desirable plants | - to preserve rare species by replicating strands that survive better in their environment and by planting many of them.

Question 69

Differentiate between pollination, fertilisation and seed dispersal.

Answer 69

Pollination: the transfer of pollen from the anthers of a flower to the stigma of the same flower or of another flower. Fertilization: the union of male and female gametes (pollen and egg), to form a zygote Seed Dispersal: the movement or transport of seeds away from the parent plant. (eg. by animals or by wind)

Question 70

Explain the mutualistic relationships with pollinators in sexual reproduction.

Answer 70

Carried from the anther to the stigma either by wind or animals. Example of mutualistic relationship: both parties benefit

Question 71

What happens when one of the species of a mutualistic relationship changes?

Answer 71

Pollination may not be possible and this could lead to extinction of both species

Question 72

How does fertilisation work in plants?

Answer 72

The pollen grain penetrates the stigma and grows a tube that grows down ovary. Ovary where the egg cell is fertilised Occurs in ovule

Question 73

How can seeds be dispersed?

Answer 73

``` Eaten by animals and excreted by faeces By wind By water Attached to the fur of animals Sometimes the whole fruit is dispersed. ```

Question 74

List the 11 structures of a flower.

Answer 74

1. Pistil 2. stigma 3. style 4. ovary 5. ovule 6. stamen 7. stamen 8. filament 9. petal 10. sepal 11. peduncle

Question 75

What does a seed normally contain? (More on notes)

Answer 75

``` Radicle Plumule One or two cotyledons Testa Hilum Micropyle ```

Question 76

List the factors that affect germination.

Answer 76

Seeds: need water, O2, light Water: uptake of water by dry seeds start the germination process Oxygen: seeds absorb Temperature: suitable for metabolic reactions