NEW BIOLOGY HL C3.1 INTEGRATION OF BODY SYSTEMS

Define tropic movement

• directional movements of the plant. dueto stimuli

Contrast positive vs. negative phototropism, and give an example

• positive phototropism = movement towards a stimulus

  • ex. phototropsim (stem grows towards the right)

• negative tropism = movement away from stimulus

  • ex. roots are negative (in terms of phototropism)

If the light source is above or lateral, what happens to the stem?

• If above = stem grows vertically up

• If lateral = plant grows towards light source

Describe positive and negative geotropism

• Roots show positive (Grow down)

• Stems show negative (grow up)

Define phytohormones and its purpose

• Plant hormones that regulate multiple physiological processes (growth, development, etc)

• Act as chemical messengers

• Secreted in almost all plant parts and transported by vascular system

List 5 types of phytohormones

1. Auxins

2. Cytokinins

3. Gibberellins

4. Abscisic acid

5. Ethylene

Describe role of auxins (IAA)

• Role: cell elongation (for tropic movements), and apical dominance (inhibit growth of lateral buds so plant grows vertically)

• Are growth hormones made mainly in shoot apical meristem (tip meristematic tissue)

  • Are transported down the stem

Describe role of cytokinins

• abundant in growing tissues

• made in roots, then pass to leaves

• role: cell division, differentiate meristem, delay senescence (aging)

Describe role of gibberellins

• made in apical meristems of roots/shoots, embryos, young leaves

• role: elongate shoot, seed germination, matures flowers/fruits, break seed dormancy, delays senescence

Describe role of abscisic acid (ABA)

• role: drops or cut off leaves

• Increases during stress (like intense cold) to stop growth

• inhibits elongation fo stems, induces seed dormancy

Auxin is mainly found in what form? Where is it made?

• As IAA (indole-3-acetic acid)

• made by shoot tips/growing regions of plants, diffuses to stem/root

What causes tropic movements?

Unequal distribution of auxin

Describe auxin movement when light source is above vs. lateral

Above

• auxin from shoot tip evenly diffuses down stem

• cells grow at same rate, so shoot grows vertically up

Lateral

• auxin moves towards shaded side, causing more rapid cell elongation at that side

• uneven growth causes stem to bend towards light source

What is polar auxin transport?

• the transport of auxins in a directional way so plants grow towards light

What is a major method of auxin transport called? What are its 2 main steps?

• the active directional cell-to-cell movement of auxin

1. Auxin enters cell passively through auxin influx carriers

2. Auxin exits the cell using auxin efflux pumps

List the 6 steps in active cell-to-cell transport

1. Auxin enters cell by difussion (facilitated by influx carriers, like AUX1/LUX1)

2. Inside the cell, IAA dissociates. The auxins (IAA-) can’t exit cell

3. Auxin efflux carriers pump out these ions using ATP —> these carriers are located on a particular side of cell so ions can flow in proper direction

4. Creates more [auxin] in apoplast and lower [auxin] in adjacent cell. Auxin flows down gradient into adjacent cell, resulting in auxin influx

5. Cells can coordinate location of carriers on the same side to accumulate it on shaded shade

6. Cells elongate on shaded side

What needs to happen for cell growth?

• Cross links between cellulose molecules of cell wall need to be broken

What is the acid growth theory?

• explains how auxin causes cell elongation

1. auxin binds to receptor proteins on membranes of cells (away from light) to activate H+-ATPases

2. H+-ATPases pump H+ fast into cell wall to lower pH

3. acidification loosens bonds between cellulose using expansins (loosens H+ bonds)

4. at the same time, K+ channels in plasma membrane open for influx into cell to lower internal water potential

5. H2O enters cells by osmosis

6. internal tugor pressure increases so cell wall stretches

What is the combined role of auxins and cytokinins?

• Regulates meristem development (developing roots or shoots)

• auxins = made by stem meristem

• auxin moves to root (causing geotropism)

• cytokinin = made by root meristem

• cytokinin moves to shoot using vascular tissues

• ratio of auxins vs. cytokinins determines root/shoot development, and also apical dominance

• more auxin = develop roots (can also inhibit lateral bud growth)

  • it travels up

• more cytokinin = develop shoot/buds (can also stimulate lateral bud growth)

  • it travels down

Describe role of ethylene

• helps fruit ripen, breaks down cell walsl tos often it, decreases bitter phenolic compounds, makes food sweeter by breaking down starch, causes fruit to change colour, gives aroma

• works based on a positive feedback mechanism (some ethylene leads to more ethylene production)

How can plants control auxin concentrations when light availability changes

• they can change the position of auxin efflux carriers, allowing auxin to move out of cells