Topic 9 Flashcards
1
Q
Define transpiration
A
The loss of water vapour from the leaves and stems of plants
2
Q
Explain why transpiration is inevitable in plants
A
- Transpiration is a consequence of gas exchange
- CO2 is necessary for plants to conduct photosynthesis
- The opening of stomata exposes xylem to the environment and allows water vapour to escape
3
Q
Explain how plants use guard cells to minimize water loss
A
- Guard cells are found in pairs, one on either side of a stoma
- Control the opening of the stoma and can adjust from wide open to fully closed
4
Q
Outline the experimental setup to measure transpiration rates
A
- Use of potometer, which measures the rate of water uptake of in a tube
- Use a ruler to measure the distance that the bubble travels in the tube in a set period of time
5
Q
Xylem
A
- Long continuous tubes
- Their walls are thickened, and the thickenings are impregnated with a polymer called lignin
- This strengthens the walls, so that they can withstand very low pressures without collapsing
- Transports water up the plant
- Made up of nonliving cells
6
Q
Explain how cohesion and adhesion allow water to be transported in xylem
A
- Water molecules are polar, and form hydrogen bonds with each other (cohesion)
- Forms a continuous stream of water molecules and pulls water up the plant when transpiration occurs
- Water molecules are also attracted to the hydrophilic part of the xylem (adhesion)
- Cell walls in leaf attracts water molecules from xylem to replace the water lost in transpiration
7
Q
Explain transpirational pull
A
- Low pressure in xylem generates a pulling force all the way down to the ends of the roots
- Strong enought to go against the force of gravity
- Passive process, with all the energy needed for it coming from the thermal energy (heat) that causes transpiration
- The pulling of water upwards in xylem vessels depends on the cohesion that exists between water molecules
- Water can stand the low pressure because it is incompressable
8
Q
Explain the process of uptaking water in the roots
A
- Solute concentration inside the root cells is greater than that in the water in the soil
- Concentration gradients are established by active transport, using protein pumps in the plasma membranes of root cells.
- There are separate pumps for each type of ion that the plant requires.
- Water follows the concnetration gradient and enters the root by osmosis
9
Q
Explain the mutualistic relationship between fungi and plants (roots)
A
- Some ions move through the soil very slowly because the ions bind to the surface of soil particles
- Plants have developed a relationship with a fungus that grows on the surface of the roots
- The fungus grows out into the soil and absorb mineral ions such as phosphate from the soil and supply the ions to the roots, allowing the plant to grow in mineral-defcient soils.
10
Q
Outline the apoplastic pathway which the water molecules enter the xylem
A
- Water molecules travels to the xylem through cell walls
- Little resistance for the water – faster transport
- Before it enters the xylem, it is blocked by the Casparian strip (waxy layer) and is forced to enter the cytoplasm to move through the endodermis
11
Q
Outline the symplastic pathway which the water molecules enter the xylem
A
- Water molecules travel through the cytoplasm of the cells
- Some resistance along the pathway
- Slightly slower, but it not blocked by the Casparian strip
12
Q
Define xerophytes
A
Plants adapted to growing in deserts and other dry habitats
13
Q
Outline the strategies that xerophytes use to survive in deserts
A
- Ephemeral (short life cycle) completed when water is available
- Increasing the rate of water uptake form the soil and reduce the rate of water loss by transpiration (reduced leaf size or rolled leaf)
- Perennial plants rely on storage of water in specialized leaves, stems or roots
- Temporal adaptation (stomata open at night) – CAM photosynthesis
14
Q
Define halophytes
A
Plants that live in saline soils
15
Q
Outline the strategies that halophytes use to survive in saline environment
A
- Leaves are reuced to small scaly structures or spines
- Leaves are shed when water is scarce, and stems become green and take over photosynthesis
- Water storage structures
- Thick cuticle and multiple layered epidermis
- Sunken stomata
- Long roots
- Structures for removing salt build-up
16
Q
Phloem
A
- Found throughout the plants
- Composed of sieve tubes (columns of specialized cells) and companion cells
- Transports orgainic compounds in both directions
17
Q
Define translocation
A
- Transport of organic solutes in a plant
18
Q
Sources
A
- Areas where sugars and amino acids are loaded into the phloem
- Photosynthetic tissues (mature green leaves, green stems)
- Storage organs that are unloading their stores (storage tissues in germinating seeds, tap roots or tubers)
19
Q
Sinks
A
- Areas where the sugars and amino acids are unloaded and used
- Roots that are growing or absorbing mineral ions using energy from cell respirations
- Parts of the plants that are growing or developing food stores (developing fruits, seeds, leaves, tap roots or tubers)
20
Q
Explain how sucrose are transported into phloem
A
- Sucrose travels through cell walls from mesophyll cells to the cell walls of companion cells, then sieve cells
- Sucrose transport protein in sieve cells actively transport the sugar in
- Proton pump uses energy to pump H+ out of companion cells
- H+ flows down the concentration graident through a co-transport protein that carry surcrose into the sieve tube complex
21
Q
How does pressure and water potential different allow transport of sucrose
A
- Build up of sucrose draw water into the companion cell through osmosis (from the nearby xylem)
- Rigid cell walls combined with the incompressibility of water result in a build-up of pressure
- Water will flow from this area of high pressure to an area of low pressure (sink)
- At the sink, sucrose is withdrawn from the phloem and water leaves the phloem and flows back to the xylem
22
Q
Explain how sieve cell’s structure help its function
A
- Sieve tubes are composed of columns of specialized cells called sieve tube cells
- Living cells with reduced cytoplasm and no nucelus
- Depend on the membrane to help maintain the sucrose and organic molecule concentration that has been established by active transport (rigid cell wall)
- Individual sieve tube cells are separated by perforated walls called sieve plates – lower resistance to the flow of phloem sap
25
Q
Label a diagram of the cross section of a stem
A
26
Q
Label a diagram of the cross section of a root
A
45
Q
Explain the two forms of phytochrome
A
- Phytochrome can switch between two forms, PR and PFR
- When PR absorb red light (660 nm), it is converted into PFR
- When PFR absorbs far-red light (730 nm), converted to PR
- Sunlight contains more red light, so in daylight, PR is rapidly converted to PFR
- PR is more stable than PFR, so PFR gradually change into PR in darkness
- PFR is the active form of phytochrome and receptor proteins bind to PFR (either inhibit or promote reproduction)
47
Q
Outline methods to induce short-day plants to flower out of season
A
- Manipulate the length of the days and nights to induce flowering
Ex) Long-day plants can flower if provided additional light in the middle of the night
55
Q
Draw and label a diagram of an animal-pollinated flower
A
56
Q
Draw and label a diagram of a seed
A
