Compilation of Plants (year 6)

Question 1

Name adaptations for gas exchange in leaves

Answer 1

Waxy cuticle - covers epidermis cells, reduce transpiration

Epidermis - Provides protection for mesophyll cells within leaf. Transparent to allow light to reach mesophyll cells

Air spaces - Facilitate the diffusion of gases btwn surrounding atmosphere and mesophyll cells

Spongy mesophyll - irregular shape increase SA:V ratio for gas exchange. Surrounded by air spaces

Stomatal guard cells - open and close stomata (pores to allow gases to enter/exit leaf)

veins - provide support. Contain xylem, phloem.

Question 2

Practice draw and label distribution of tissues in a transverse section of a dicot leaf

Answer 2

Include
- wax cuticle
- upper/lower epidermis
- palisade, spongy mesophyll
- air space
- chloroplats
- stomata
- guard cells

Question 3

Factors affecting transpiration

Answer 3

Light intensity increases = more stomata open = increased transpiration

Temperature increase = water particles gain kinetic energy, move faster = diffuse through stomata at a higher rate + higher temperatures increase rate of evaporation = increased transpiration

Humidity increase = conc of water outside increase = decrease conc. gradient = diffuse slower = decreased transpiration

Air flow increase = move water vapour away from leaf = reduce conc outside stomata = increase conc gradient = increase transpiration

Question 4

Describe transpirational pull

Answer 4

Loss of water by transpiration from mesophyll cells through the stomata causes water to be drawn out of xylem vessels and through cells walls by capilllary action, generating tension and a -ve pressure in the leaf.

Water enters the root by osmosis and moves into the xylem in the roots, creating a higher pressure.

this tension in the leaves draws water up the xylem. Cohesion (due to H-bonds) ensures it is a continuous column of water. Adhesive properties of water allow it to form H-bonds with the cellulose in cell wall, maintain movement of water up the xylem

Question 5

Adaptations of xylem vessels for transport of water

Answer 5

• xylem vessels are dead, hollow, no cell contents or plasma membrane, allowing for unimpeded flow of transpiration stream
• absent end walls for unimpeded flow
• lignified walls to withstand tensions and inward pressures created by transpiration, provide structural support for the stems of plants
• pits for entry, exit of water

Question 6

Draw, label diagram of transverse section of a dicot plant stem + describe their function

Answer 6

Include:
- vascular bundles (contains xylem and phloem tissue)
- xylem (transport water, minerals up stem)
- phloem, (transport organic compounds e.g. sucrose, amino acids, up/down the stem)
- cortex (provide structural support, stores starch in root of plants)
- epidermis (protection for stem)

Question 7

Draw + label tissues in transverse section of root of dicot plant

Answer 7

include:
- vascular bundles
- xylem and phloem
- cortex
- epidermis

Question 8

What is phototropism

Answer 8

Plants display postive phototropism as a directional growth towards light sources.

• plants are sessils and cannot relocate, so this positive phototropism enables plants to adapt to their environement

Question 9

What phytohormones are found in plants + function

Answer 9

Auxin - plant cell elongation
cytokinin - increase rate of cell division
Ethylene - promote fruit ripening
Gibberellin - control stem elongation, seed germination, flowering, dormancy

Question 10

how is auxin transported

Answer 10

• Auxins can diffuse into plant cells, but is modified in the cell such that it cannot diffuse out
• Auxin is actively transported out through protein pumps in the plasma membrane called AUXIN EFFLUX CARRIERS
• plant cells in a shoot can coordinate the prodction of auxin efflux carriers on the same size, such that auxin is actively transported until there is high conc. on one side of the plant
• this high conc can promote uneven cell elongation for phototropism, gravitropism

Question 11

How does auxin promote cell growth?

Answer 11

• Auxin promotes the synthesis and membrane insertion of proton pumps, which use ATP to move H+ out of the cell into the apoplast
• this acidifies the cell wall, lowering pH
• the lower pH activates expansin, a protein that disrupts H-bonds btwn cellulose fibres
• Expansin loosen cross links btn cellulose molecules, allowing them to slide into new positions.
• increased water absorption generates turgor pressure, driving fiber movement.
• cellulose fibres form new H-bonds in their adjusted positions, resulting in elongated cells.

Conc. gradients of auxin cause the differences in growth rate needed for phototropism

Question 12

How do auxin and cytokinin regulate plant growth

Answer 12

Root tips produce cytokinin, which is tranported in xylem fluid to shoots.

Shoot tips produce auxin, which is transported within sap in phloem to roots.

At certain conc. these 2 hormones work synergistically with each other. Best plant growth is when growing tips of shoots and roots have access to both cytokinin (for cell division) and auxin (for cell elongation)

Question 13

Describe +ve feedback in fruit ripening and ethylene production

Answer 13

Ethylene stimulates the changes in fruits that occur during ripening.
Ripening also stimulates increased production of ethylene.

This +ve feedback ensures fruit ripening is rapid and synchronized.