Topic 9

Question 1

Sieve elements

Answer 1

sieve elements form tubes which transport water & solutes

- to be efficient at transport, they have reduced quantities of the cytoplasm and have no nucleus, ribosomes or vacuole

Question 2

Fibres of Sclerenchyma cells

Answer 2

provide structural support for the plant

Question 3

Paranchyma

Answer 3

acts as a packaging material between other cell types & helps transfer materials to the sieve elements & companion cells

Question 4

Companion cells

Answer 4

are “life support” for the sieve element cells as they perform certain metabolic functions for sieve elements
- also why plasmodesmata(microscopic pores in the cell walls) between companion cells & sieve element cells are larger than in most plant cells to allow for the exchange of metabolites (e.g ATP)

Question 5

How are sieve tubes structured to its function?

Answer 5

• Rigid cell walls of sieve tube
  → allow for the building of high pressures needed to generate hydrostatic pressure (the flow inside the tubes)
• The ends of sieve element cells are connected with other sieve elements together to form a sieve tube
• Sieve plates are found

Question 6

What is hydrostatic pressure?

Answer 6

the pressure exerted by a liquid due to the force of gravity

- in the phloem it causes the sugar & the water to be pushed towards the source cell (translocation)

Question 7

What are the functions of transpiration?

Answer 7

• carries water to various parts of the plant
• carries minerals along w the water
• cools down the plant when water evaporates through the stomata

Question 8

cuticle

Answer 8

• protects the plant against water loss & insects
• if no cuticle is present, the epidermis protects the leaf
• waxy, so its good for water loss prevention

Question 9

Epidermis

Answer 9

• provides a protective barrier if no cuticle is present

- flat, tightly packaged cells on the leaf

Question 10

Palisade mesophyll

Answer 10

• cells that are near the top of the leaf that are most responsible for light absorption & photosynthesis (why they are at the top & not the bottom)
• contain a lot of chloroplast (bc thats what’s needed for photosynthesis)

Question 11

Spongy mesophyll

Answer 11

• a layer of sparsely spaced cells where there are channels for gas exchange
• air pockets allow for efficient gas exchange ->the gases that are coming in & out of the cell are oxygen & carbon dioxide

Question 12

What is the rate of transpiration in xerophytes & why?

Answer 12

Xerophytes will have high rates of transpiration due to the high temperatures and low humidity of desert environments

Question 13

What are xerophytes?

Answer 13

Xerophytes are plants that can tolerate dry conditions (such as deserts) due to the presence of a number of adaptations

Question 14

What are the adaptions of xerophytes?

Answer 14

• Reduced leaves
• rolled leaves
• thick, waxy cuticle
• stomata in pits
• low growth
• CAM physiology

Question 15

What are halophytes?

Answer 15

Halophytes are plants that can tolerate salty conditions (such as marshlands) due to the presence of a number of adaptations

Question 16

What are the adaptions of halophytes?

Answer 16

• Cellular sequestration
• Tissue partitioning
• root level exclusion
• salt excretion
• altered flowering schedule

Question 17

What is a photometer?

Answer 17

a device that is used to estimate transpiration rates by measuring the rate of water loss / uptake

Question 18

What are the models of water transport?

Answer 18

• capillary tubing
• filter paper
• porous pots

Question 19

Capillary tubing

Answer 19

• Water has the capacity to flow along narrow spaces in opposition to external forces like gravity (capillary action)
• This is due to a combination of surface tension (cohesive forces) and adhesion with the walls of the tube surface
• The thinner the tube or the less dense the fluid, the higher the liquid will rise (xylem vessels are thin: 20 – 200 µm)

Question 20

Filter paper

Answer 20

• Filter paper (or blotting paper) will absorb water due to both adhesive and cohesive properties
• When placed perpendicular to a water source, the water will hence rise up along the length of the paper
• This is comparable to the movement of water up a xylem (the paper and the xylem wall are both composed of cellulose)

Question 21

Porous pots

Answer 21

• Porous pots are semi-permeable containers that allow for the free passage of certain small materials through pores
• The loss of water from the pot is similar to the evaporative water loss that occurs in the leaves of plants
• If the porous pot is attached by an airtight seal to a tube, the water loss creates a negative pressure that draws more liquid

Question 22

What is translocation?

Answer 22

is the movement of organic compounds (e.g. sugars, amino acids) from sources to sinks

Question 23

What is a source?

Answer 23

a source is where organic compounds are synthesised - this is the photosynthetic tissue (e.g leaves)

Question 24

What is the sink?

Answer 24

the sink is where the compounds are delivered to for use or storage - this includes roots, fruits & seeds

Question 25

Why are sugars transported as a disaccharide?

Answer 25

transported as sucrose bc it is soluble but metabolically inert

Question 26

What are aphids?

Answer 26

are a group of insects, belonging to the order Hemiptera, which feed primarily on sap extracted from phloem

Question 27

What are the factors affecting translocation rate?

Answer 27

- the rate of photosynthesis - the rate of cellular respiration - the rate of transpiration - the diameter of the sieve tubes

Question 28

What are meristems?

Answer 28

Meristems are tissues in a plant consisting of undifferentiated cells capable of indeterminate growth

Question 29

What is micropropagation?

Answer 29

Micropropagation is a technique used to produce large numbers of identical plants (clones) from a selected stock plant

Question 30

Micropropagation is used to rapidly produce large numbers of cloned plants under controlled conditions:

Answer 30

- rapid bulking - virus free strains - propagation of rare species

Question 31

Rapid Bulking

Answer 31

- Desirable stock plants can be cloned via micropropagation to conserve the fidelity of the selected characteristic - This process is more reliable that selective breeding because new plants are genetically identical to the stock plant - This technique is also used to rapidly produce large quantities of plants created via genetic modification

Question 32

Virus-free strains

Answer 32

- Plant viruses have the potential to decimate crops, crippling economies and leading to famine - Viruses typically spread through infected plants via the vascular tissue – which meristems do not contain - Propagating plants from the non-infected meristems allows for the rapid reproduction of virus-free plant strains

Question 33

Propagation of Rare Species

Answer 33

- Micropropagation is commonly used to increase numbers of rare or endangered plant species - It is also used to increase numbers of species that are difficult to breed sexually (e.g. orchids) - It may also be used to increase numbers of plant species that are commercially in demand

Question 34

What is pollination?

Answer 34

- The transfer of pollen grains from an anther (male plant structure) to a stigma (female plant structure)

Question 35

What is fertilisation?

Answer 35

- Fusion of a male gamete nuclei with a female gamete nuclei to form a zygote

Question 36

What is seed dispersal?

Answer 36

- Fertilisation of gametes results in the formation of a seed, which moves away from the parental plant

Question 37

What is the stamen composed of?

Answer 37

- anther | - filament

Question 38

What is the pistil (or carpel) composed of?

Answer 38

- stigma - style - ovule

Question 39

Anther

Answer 39

- pollen producing organ of the flower (pollen is the male gamete of a flowering plant)

Question 40

Filament

Answer 40

- slender stalk supporting the anther (makes the anther accessible to pollinators)

Question 41

Stigma

Answer 41

- the sticky, receptive tip of the pistil that is responsible for catching the pollen

Question 42

Style

Answer 42

the tube-shaped connection between the stigma and ovule (it elevates the stigma to help catch pollen)

Question 43

Ovule

Answer 43

the structure that contains the female reproductive cells (after fertilisation, it will develop into a seed)

Question 44

Petals

Answer 44

function to attract pollinators

Question 45

Sepal

Answer 45

Outer covering which protects the flower when in bud

Question 46

What are phytochromes?

Answer 46

Phytochromes are leaf pigments which are used by the plant to detect periods of light and darkness

Question 47

What is photoperiodism?

Answer 47

The response of the plant to the relative lengths of light and darkness

Question 48

Phytochromes exist in two forms – an active form and an inactive form:

Answer 48

- The inactive form of phytochrome (Pr) is converted into the active form when it absorbs red light (~660 nm) - The active form of phytochrome (Pfr) is broken down into the inactive form when it absorbs far red light (~725 nm) Additionally, the active form will gradually revert to the inactive form in the absence of light (darkness reversion)

Question 49

Why is the active form predominant during the day?

Answer 49

Because sunlight contains more red light than moonlight, the active form is predominant during the day - Similarly, as the active form is reverted in darkness, the inactive form is predominant during the night

Question 50

What will a typical seed possess?

Answer 50

- testa - micropyle - cotyledon - plumule - radicle

Question 51

Testa

Answer 51

an outer seed coat that protects the embryonic plant

Question 52

Micropyle

Answer 52

a small pore in the outer covering seed, that allows for the passage of water

Question 53

Cotyledon

Answer 53

contains the food stores for the seed and forms the embryonic leaves

Question 54

Plumule

Answer 54

the embryonic shoot (also called the epicotyl)

Question 55

radicale

Answer 55

the embryonic root

Question 56

For germination to occur, a seed requires a combination of:

Answer 56

- oxygen - temp - water - pH

Question 57

How can germination be measured?

Answer 57

germination can be measured by the rate of seed growth over a set period of time