AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Some of the substances transported in and out of cells by diffusion are…
Full specification wording
Diffusion: Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney.
Diffusion moves several important substances into and out of cells.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 3 of 11
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Diffusion moves several important substances into and out of cells. In gas exchange, oxygen diffuses into cells because it is used in respiration, while carbon dioxide, a waste product of respiration, diffuses out of cells. In the lungs, oxygen diffuses from the air into the blood and carbon dioxide diffuses from the blood into the air. Urea is a waste product made in the liver from the breakdown of excess amino acids. It diffuses from cells into the blood plasma and is carried to the kidneys, where it is removed from the blood and excreted in urine. The statement is assessed by asking you to name these substances and explain the direction of their diffusion in relation to their source and destination.
What earns the marks
- Oxygen diffuses into cells and is used in respiration.
- Carbon dioxide is produced by respiration and diffuses out of cells.
- In gas exchange, oxygen and carbon dioxide diffuse between an organism and its environment, for example in the lungs.
- Urea is a waste product formed from the breakdown of excess amino acids.
- Urea diffuses from cells into the blood plasma.
- Urea is transported to the kidney and excreted, so diffusion is part of the route to excretion.
Common mistakes and how to put them right
Saying carbon dioxide diffuses into cells for respiration.
Put it right: Carbon dioxide is a waste product of respiration and diffuses out of cells.
Stating that urea is excreted by diffusion in the kidney.
Put it right: Urea diffuses into the blood plasma and the kidney removes it from the blood for excretion.
Confusing gas exchange with respiration.
Put it right: Gas exchange is the diffusion of oxygen and carbon dioxide, while respiration is the chemical process that uses oxygen and produces carbon dioxide.
Exam tips
- Name the substance, its starting region and its destination to show the direction of diffusion clearly.
- Link oxygen and carbon dioxide to respiration so the reason for their movement is clear.
- For urea, state that it moves into the blood plasma and is then excreted by the kidney.
Try the lesson
The start of the Diffusion: Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney. lesson, made from checked teaching notes for this specification point.
Have a go first
Which waste product diffuses out of cells into the blood plasma to be excreted by the kidneys?
Listen
Diffusion moves several important substances into and out of cells. In gas exchange, oxygen diffuses into cells because it is used in respiration, while carbon dioxide, a waste product of respiration, diffuses out of cells. In the lungs, oxygen diffuses from the air into the blood and carbon dioxide diffuses from the blood into the air. Urea is a waste product made in the liver from the breakdown of excess amino acids. It diffuses from cells into the blood plasma and is carried to the kidneys, where it is removed from the blood and excreted in urine. The statement is assessed by asking you to name these substances and explain the direction of their diffusion in relation to their source and destination. A strong answer earns marks for these points. Oxygen diffuses into cells and is used in respiration. Carbon dioxide is produced by respiration and diffuses out of cells. In gas exchange, oxygen and carbon dioxide diffuse between an organism and its environment, for example in the lungs. Urea is a waste product formed from the breakdown of excess amino acids. A common slip: Saying carbon dioxide diffuses into cells for respiration. Instead, carbon dioxide is a waste product of respiration and diffuses out of cells. Exam tip: Name the substance, its starting region and its destination to show the direction of diffusion clearly.
Key words
Say what each word means before you turn the card.
Gas exchange
Try answering aloud or in your head before turning the card.
Respiration
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See every definition
- Gas exchange
- The diffusion of oxygen and carbon dioxide between an organism and its environment, for example in the lungs.
- Respiration
- The chemical process that uses oxygen and produces carbon dioxide.
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