Growth in plants Flashcards
1
Q
What allows and is indeterminate growth?
A
- The ability to grow throughout their lives, this is due to the undifferentiated cells in the meristem than produce new cells
- Growth is concentrated in the meristem at the tip of roots
- Meristems are made out of undifferentiated cells that can grow through mitosis and cell division rapidly
2
Q
Where does growth occur?
A
- At the apex (top), where new cells are formed remain meristematic, other cells elongate and then begin to specialize in the zone of differentiation
- These areas of growth are called apical meristems (the apex or tip of the root/shoot)
3
Q
What does mitosis and cell division mean for growth?
A
- Mitosis and cell division in the shoot apical meristem produces cells to increase the length of the organ of the plant and develop them further
4
Q
What do apical meristems do?
A
- The apical meristem gives rise to other partially differentiated tissues that can further differentiate
- The apical meristem also creates dormant meristems in the axillary buds (where leaf and stem join)
- Response to stimuli (sensitivity) may lead to changing the number of cells produced by the meristem
- Growth of apical meristems is also called primary growth
5
Q
What do plant hormones do?
A
- Hormones are chemical messengers that carry information from one cell of an organism to another
- In plants they are transported in the sap
6
Q
What is auxin and what does it do?
A
- A hormone synthesised in the apical meristem and travels down the stem which causes cell elongation and inhibits the growth of axillary (side) buds
- The further it travels, the lower the concentration becomes
7
Q
What is apical dominance?
A
- When auxins inhibit the growth of the axillary buds which causes the plant to grow vertically upward to trap more light
- When the shoot apex is far away from the axillary bud and the auxin concentration becomes too low, the bud begins to develop again (branches)
8
Q
What is plant tropism?
A
- Tropism: directional growth in response to an external stimulus, plants respond to there stimuli by tropism
- Phototropism: response to light
- Gravitropism: response to gravity
- Positive is growth towards the stimuli and negative is growth away from it
9
Q
How do shoots and roots respond use tropism?
A
- Shoots: Positive phototropism and negative gravitropism for maximum light energy
- Roots: Positive gravitropism and negative phototropism for max water and mineral absorption
Other types of tropism: chemotropism, hydrotropism, thigotropism (touch)
10
Q
How to auxins respond to light?
A
- When light is overhead, auxins at the shoot apex diffuse evenly down the stem
- As the cells grow at the same rate, the shoot extends vertically upward
- When the position of the light changes, the auxins accumulate on the side with least light which means there is a higher concentration and therefore grows faster
- The shoot bends towards the light source
Check book
11
Q
How do auxins respond to gravity?
A
- When a phototropic response is made, the growth of cells in the root is inhibited
- The auxins accumulate on the lower shaded side
- Cell elongation is inhibited in the shaded root cells, the cells on the upper side elongate and hence the root bends towards gravity (away from light)
- Positive gravitropism and negative phototropism
12
Q
How is auxin moved from cell to cell?
A
- Either through the sap in the phloem OR
- When the light intensity is equal, auxins move downward and are pumped into and out of successive layers of cells through specialized protein pumps
- The cells have auxin influx carriers in the apical membranes and auxin efflux carriers in the basal membranes
- This makes sure that auxin moves continually downward, leads to even cell growth and extension of the stem
13
Q
What happens when the light intensity is varied?
A
- Auxin efflux carriers increase on the internal side membrane and the auxins are transported to the shades side of the plant, creates concentration gradient
- This triggers responses such as cell elongation
14
Q
What responses might occur after auxins accumulate on the shaded side?
A
- Auxins alter gene expressions, for example transcription of genes that produce proton pumps may be changed
- Auxins stimulate cell elongation in the stem. The pattern of gene expression is altered
15
Q
How does cell elongation in the stem occur?
A
- A proton pump is stimulated by auxins, which moves H+ ions into the cell wall
- A higher concentration in the cell walls means it becomes more acidic which breaks the bonds between cellulose fibers in the cell wall
- Reduced number of bonds makes the cell wall more flexible and the turgor pressure slides the cellulose fibers further apart, thus cell elongation occurs
16
Q
What is micropropagation?
A
- A technology that uses plant’s flexible growth patterns to produce many clones from an original plant (plant cells are totipotent and can give rise to an entire organism)
- A tissue sample from the shoot apical meristem is sterilized to promote cell growth but not differentiation
- This gives rise to a callus (large mass of undifferentiated cells) which are separated and placed into different medium to trigger cell differentiation and development
17
Q
What are the advantages of micropropagation?
A
- Allows rapid increase in number of plants
- Production of virus-free individuals of existing varieties, newly produced cells don’t get affected by virus of parent cell (uninfected)
- Allows the production of orchids and other rare species, bypasses issues
