Ch 9.3

Question 1

Meristems

Answer 1

• undifferentiated cells in the meristems of plants allow indeterminate growth
• areas of a plant that are undergoing mitosis and thus growing
• found in the tip of the shoot (stem) and the tips of the root
• these areas can continue to grow and thus elongate throughout the plant’s life

Question 2

Stem apical meristem

Answer 2

• more complex than the root meristem as it needs to develop into stems, leaves or flowers, depending on the needs of the plant
• each time it goes through mitosis, two cells are made. One remains a part of the meristem, the other develops into stem, leaf or flower cells.

Question 3

What is a hormone?

Answer 3

-a hormone is a chemical message that is produced and released in one part of an organism to have an effect in another part of an organism

Question 4

What is auxin?

Answer 4

• a hormone that is made and released from shoot apical meristem
• acts on many different cells in plant
• influences cell growth rates by changing the pattern of gene expression

Question 5

What are some things that auxin controls?

Answer 5

• in low amounts, promotes the growth of roots
• in high amounts, inhibits the control of roots
• in medium amounts, promotes the growth of stems
• in high amounts, inhibits the growth of stems

Other things:

• influences development of fruits
• regulates leaf development
• controls growth of the shoot apex
• promotes cell elongation
• promotes development of vascular tissue
• causes leaves to drop when they are no longer needed

Question 6

Tropism

Answer 6

-directional growth response to external stimuli

Question 7

List two different examples of tropism

Answer 7

• phototropism

- gravitropism

Question 8

Phototropism

Answer 8

• growth towards or away from light
• stem grows towards light (positively phototropic)
• roots grow away from light (negatively phototropic)

Question 9

Gravitropism

Answer 9

• growth towards or away from gravity
• stems grow away from gravity (negatively gravitropic)
• stems grow toward gravity (positively gravitropic)

Question 10

How does phototropism work?

Answer 10

• when plants absorb light, chemicals in the plant called phototropins change shape
• the phototropins then bind to receptors in cells and change which genes are being used by the plant cell
• this changes growth in the cell
• if the phototropins in the tip detect a greater intensity of light on one side of the stem than the other, auxin is transported laterally from the side with brighter light to the more shaded side
• higher concentrations of auxin on the shadier side builds and triggers the cell membranes to let more salts in, thus triggering osmosis causing the cells to swell and elongate.
• the stem grows in a curve towards the source of the brighter light

Question 11

How does gravitropism work?

Answer 11

• gravity causes a release of auxin
• in the roots auxin builds up on the bottom of the root
• this build-up of auxin inhibits the growth in the bottom, causing the top to bend down and the roots grow in the direction of gravity

Question 12

Micropropagation

Answer 12

• in vitro procedure that produces large numbers of identical plants
• works because many cells in plants are totipotent
• able to divide and become any functional plant part
• tissues from desired plant are sterilized and cut into small pieces
• pieces are then placed in sterilized growth media that includes plant hormones such as auxin and cytokinin
• if auxin > 10x cytokinin: roots develop
• if auxin < 10x cytokinin: shoots develop
• once roots and shoots develop, plant can be transferred to soil

Question 13

What are the benefits of micropropagation?

Answer 13

1. Allows growers to quickly make identical copies of desired plants
   - rapid bulking up of new varieties
   - production of virus-free strains of existing varieties
2. Faster and takes up less space than traditional methods of cultivation
3. Can allow for the production of lots of endangered/rare plants to protect them.
   - propagation of orchids/other rare species