9.3 (Plant Biology)

Question 1

Define indeterminate growth and totipotent.

Answer 1

indeterminate growth- where the plant will continue adding new organs (leaves, stems, roots) as long as it has access to the necessary resources.
totipotent: capable of giving rise to any cell type or (of a blastomere) a complete embryo.

Question 2

State that most plants have indeterminate growth and have totipotent cells.

Answer 2

most plants have indeterminate growth and have totipotent cells.

Question 3

Define meristem.

Answer 3

Plant tissue that remains embryonic as long as the plants lives, allowing for indeterminate growth

Question 4

Compare apical and lateral meristems.

Answer 4

Apical meristem: primary growth (length), occurs at tip of shoots and roots, produces new leaves and flowers.
Lateral meristem: secondary growth (wide), occurs at the cambian (between xylem/phloem), produces bark on trees.

Question 5

Outline role of mitosis in the growth of stem and leaves while maintaining a meristem.

Answer 5

Apical meristem gives rise to growth (length), thus goes through the cell cycle to produce more cells by mitosis and cytokinesis.
Every division results in one cell REMAINING at the meristem whilst the other one grows and differentiates as it gets pushed away from the meristem. (Differentiation gives rise to many different tissues > vascular tissue, leaves or flowers.)

Question 6

State the generic function of plant hormones.

Answer 6

Plant Hormones are the plant growth regulators. They require in small amount but necessary for functioning of Plants.

Question 7

Outline how auxin concentrations regulate plant growth in the root and stem.

Answer 7

Auxin activates proton pumps H+ gene expression, which means acidity loosen cell walls. Auxin activates expansion, which also means gene express = protein loosen cell walls.

Question 8

Outline the role of auxin in apical dominance.

Answer 8

Auxin has a role in stimulating growth at the shoot apex, inhibiting lateral shoot growth which is apical dominance.

Question 9

State two external factors that control the growth of roots and stems.

Answer 9

Light and gravity

Question 10

Define tropism, phototropism and gravitropism.

Answer 10

Tropism: growth in response to a stimuli
Phototropism: growth in response to light
Gravitropism: growth in response to gravity

Question 11

Explain how auxin concentrations allow for phototropism in the stem.

Answer 11

At the stems, auxins stimulates cell growth.

•PIN3 transport auxins to shady side, thus plants elongates on shade side, towards the sun. (Phototropism)

Question 12

Explain how auxin concentrations allow for gravitropism in the root.

Answer 12

At the roots, auxins inhabits cell growth. PIN3 transports auxins to gravity pull.

Question 13

State that auxin influences cell growth rates by changing gene expression.

Answer 13

In the shoots, auxin stimulates cell elongation and thus high concentrations of auxin promote growth (cells become larger) In the roots, auxin inhibits cell elongation and thus high concentrations of auxin limit growth (cells become relatively smaller)

Question 14

Explain the mechanism of auxin action in plant shoots

Answer 14

In shoots, auxin increases the flexibility of the cell wall to promote plant growth via cell elongation

• Auxin activates a proton pump in the plasma membrane which causes the secretion of H+ ions into the cell wall
• The resultant decrease in pH causes cellulose fibres within the cell wall to loosen (by breaking the bonds between them)
• Additionally, auxin upregulates expression of expansins, which similarly increases the elasticity of the cell wall
• With the cell wall now more flexible, an influx of water (to be stored in the vacuole) causes the cell to increase in size

Question 15

Define micropropagation.

Answer 15

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

Question 16

Outline how changing auxin and cytokinin ratios can lead to development of roots or shoots from the same explant tissue.

Answer 16

1) Tissue sample is collected from parent at the least differentiated part.
2) Tissue samples are placed in agar growing medium containing nutrients and auxins/cytokinin.
(If there’s more auxin, root develops; if there’s more cytokinin, shoot develops)

Question 17

Outline three roles of micropropagation of plant species.

Answer 17

1) Rapid bulking: micropropagation is more rapid and reliable in terms of cloning a desired plant than traditional techniques.
2) Virus-free strains: plant virus can decimate crops and lead to famine, but their way of transport is through vascular tissue, propagation can be done from the non-infected meristem region.
3) Rare species: micropropagation is commonly used to increase numbers of rare and endangered plants such as orchids.