(a) Explain briefly four factors… | Biology

Question 1 Report

(a) Explain briefly four factors that affect the diffusion of substances.

(b) Explain the following terms:
(i) active transport
(ii) transpiration.

(d) State the features of red blood cells and how these features adapt the cell to perform its functions.

Answer

(a) Four factors that affect the diffusion of substances

Concentration gradient - the steeper the difference in concentration between two regions, the faster the rate of diffusion.
Temperature - a rise in temperature increases the kinetic energy of the particles, so they move and diffuse faster.
Surface area - the larger the surface area over which diffusion occurs, the faster the rate.
Distance / thickness of the membrane - the shorter the distance (thinner the membrane), the faster the diffusion (the size and molecular weight of the diffusing particles also matter: small, light particles diffuse faster).

(b) Explanation of terms

(i) Active transport - The movement of substances across a cell membrane against a concentration gradient (from a region of lower to higher concentration) using energy released from respiration (ATP).
(ii) Transpiration - The loss of water in the form of water vapour from the aerial parts of a plant, mainly through the stomata of the leaves.

(c) Four ways plants reduce a high rate of transpiration

Reducing the number of stomata, and having sunken stomata in pits.
Having a thick waxy cuticle on the leaf surface.
Reducing the leaf surface area or reducing leaves to spines/scales.
Closing the stomata (especially during the hottest part of the day) and shedding leaves in the dry season; presence of hairs on the leaf surface also helps.

(d) Features of red blood cells and how they adapt the cell to its functions

Feature	How it adapts the cell to its function
Biconcave disc shape	Provides a large surface area to volume ratio for rapid uptake and release of oxygen
Contains the pigment haemoglobin	Combines readily with oxygen (as oxyhaemoglobin) to transport it round the body
Has no nucleus (in mammals)	Leaves more room inside the cell to carry more haemoglobin (and oxygen)
Small size and flexible (elastic) membrane	Allows the cell to squeeze through narrow capillaries to deliver oxygen to tissues

Answer Details

(a) Four factors that affect the diffusion of substances

Concentration gradient - the steeper the difference in concentration between two regions, the faster the rate of diffusion.
Temperature - a rise in temperature increases the kinetic energy of the particles, so they move and diffuse faster.
Surface area - the larger the surface area over which diffusion occurs, the faster the rate.
Distance / thickness of the membrane - the shorter the distance (thinner the membrane), the faster the diffusion (the size and molecular weight of the diffusing particles also matter: small, light particles diffuse faster).

(b) Explanation of terms

(i) Active transport - The movement of substances across a cell membrane against a concentration gradient (from a region of lower to higher concentration) using energy released from respiration (ATP).
(ii) Transpiration - The loss of water in the form of water vapour from the aerial parts of a plant, mainly through the stomata of the leaves.

(c) Four ways plants reduce a high rate of transpiration

Reducing the number of stomata, and having sunken stomata in pits.
Having a thick waxy cuticle on the leaf surface.
Reducing the leaf surface area or reducing leaves to spines/scales.
Closing the stomata (especially during the hottest part of the day) and shedding leaves in the dry season; presence of hairs on the leaf surface also helps.

(d) Features of red blood cells and how they adapt the cell to its functions

Feature	How it adapts the cell to its function
Biconcave disc shape	Provides a large surface area to volume ratio for rapid uptake and release of oxygen
Contains the pigment haemoglobin	Combines readily with oxygen (as oxyhaemoglobin) to transport it round the body
Has no nucleus (in mammals)	Leaves more room inside the cell to carry more haemoglobin (and oxygen)
Small size and flexible (elastic) membrane	Allows the cell to squeeze through narrow capillaries to deliver oxygen to tissues

(a) Explain briefly four factors that affect the diffusion of substances. (b) Explain the following terms: (i) active transport (ii) transpiration. (c) Stat...