gas exchange in plants

Question 1

what is the internal structure of the leaf

Answer 1

• cuticle
• palisade mesophyll
• air space
• bundle sheath cells
• xylem
• phloem
• spongy mesophyll
• stoma
• guard cell
• upper epidermis
• lower epidermis

Question 2

how does a leaf enable efficient gas exchange

Answer 2

• thin and flat, with a large surface area
• has large air spaces which allow circulation of gases
• smaller air spaces between cells of other tissues
• stomatal pores are present and can open for gas exchange

Question 3

what is the pathway of gases

Answer 3

• the gas diffuses through the stomata down a concentration gradient
• the gas then diffuses through the intracellular spaces between the mesophyll cells
• gases dissolve in the film of water covering the cells and in the cellulose cell wall
• the gas diffuses into the cell

Question 4

what happens during the daylight

Answer 4

• photosynthesis is dominant
• carbon dioxide diffuses in
• oxygen diffuses out

Question 5

what happens in the darkness

Answer 5

• respiration is dominant
• oxygen diffuses in
• carbon dioxide diffuses out

Question 6

what are some leaf adaptations for harvesting light

Answer 6

• they have a large surface area to capture as mush light as possible
• they can move slowly and are held in fixed positions
• the cuticles and epidermis are transparent
• the leaves are thin to allow a short diffusion pathway

Question 7

what are the adaptations of a palisade cell

Answer 7

• they are elongated
• densely packed
• small air spaces between them
• contain many chloroplasts
• chloroplasts can move in cells to collect the most light or move away from strong light to avoid damage

Question 8

describe the cuticle

Answer 8

• secreted by the epidermal cells
• it is waxy so acts as a waterproofing agent to prevent water loss
• covers both the upped and lower epidermis except the stomata
• prevents gas exchange
• the stomata allow both water and gases through

Question 9

what is turgor

Answer 9

• the guard cells can change shape
• when water flows into the cell, the guard cells become turgid and curve away from each other
• the inner wall is thicker and inelastic compared to the outer wall

Question 10

how do guard cells work in the daylight

Answer 10

• potassium ions move into the guard cells via active transport
• starch is converted into malate which lowers the water potential of the cell
• water flows into the guard cells down the water concentration gradient
• turgor increases and the guard cells change shape opening the stomata

Question 11

how do the guard cells work in the darkness

Answer 11

• potassium ions diffuse out of the guard cells
• malate is converted into starch
• this raises the water potential of the cell
• water flows out of the guard cells down the water potential gradient
• turgor of the cell reduces, the guard cells change shape and the stomata close

Question 12

what are xerophytes

Answer 12

• they are plants which are adapted to survive in very dry conditions
• they have physical and physiological adaptations
• they close their stomata during the day to reduce water loss

Question 13

what are the physical adaptations of xerophytes

Answer 13

• the leaves are reduced to needles or spines
• they have curled leaves
• they have sunken stomata
• they have hairy leaves
• they have shallow roots covering a large area