Name the three processes by which substances are transported into and out of cells.

Diffusion Osmosis Active transport

The net movement of particles of a gas or a dissolved substance from an area of higher concentration to an area of lower concentration.

Is diffusion an active or a passive process?

Passive – it does not require energy from the cell; particles move using their own kinetic energy.

Why is the cell membrane described as partially permeable ?

It lets some substances diffuse through but not others. For example, oxygen and carbon dioxide can pass through, but large molecules such as starch cannot.

Give two substances that diffuse into cells and say why.

Oxygen – needed for aerobic respiration Carbon dioxide – needed by plant cells for photosynthesis

Give two waste substances that diffuse out of cells.

Urea (from the breakdown of amino acids) Carbon dioxide (from aerobic respiration)

In diffusion, there is a net movement of particles from a region of higher concentration to a region of concentration.

In diffusion, there is a net movement of particles from a region of higher concentration to a region of lower concentration.

What three factors affect the rate of diffusion?

The concentration gradient (difference in concentrations) The temperature The surface area of the membrane

How does a steeper concentration gradient affect the rate of diffusion?

The greater the difference in concentration, the faster the rate of diffusion.

How does increasing the temperature affect the rate of diffusion?

The rate increases , because particles gain more kinetic energy and move faster.

How does a larger surface area affect the rate of diffusion?

A larger surface area gives a faster rate of diffusion.

Why is a single-celled organism's surface area to volume ratio described as large?

Its surface area is large compared with its small volume, so substances only travel a short distance – diffusion alone is enough to meet its needs.

As an organism gets larger, its surface area to volume ratio .

As an organism gets larger, its surface area to volume ratio decreases .

Calculate the surface area to volume ratio of a cube with sides of 2 cm.

Surface area = 6 × (2 × 2) = 24 cm 2 Volume = 2 × 2 × 2 = 8 cm 3 Ratio = 24 : 8 = 3 : 1

Why do large organisms need exchange surfaces and transport systems?

They have a small surface area to volume ratio , so diffusion alone is too slow to supply all their cells.

Why can't multicellular organisms rely on diffusion across their outer surface alone?

They have a small surface area to volume ratio and a large diffusion distance, so diffusion alone cannot supply substances fast enough for all their cells.

What features make an exchange surface efficient?

A large surface area A thin membrane (short diffusion path) A good blood supply (in animals) Being ventilated (for gas exchange in animals)

How is the small intestine adapted for exchange?

Villi give a large surface area Wall only one cell thick – short diffusion distance Good blood supply maintains the concentration gradient

How are the alveoli in the lungs adapted for gas exchange?

Millions of alveoli give a large surface area Walls one cell thick and moist – short diffusion path Good blood supply and ventilation maintain the concentration gradient

How are fish gills adapted for gas exchange?

Many filaments and lamellae give a large surface area Good blood supply maintains the concentration gradient

How are plant roots and leaves adapted for exchanging materials?

Roots: branched, with root hair cells that increase surface area for absorbing water and mineral ions Leaves: stomata and air spaces allow gases to diffuse in and out over a short distance

A good exchange surface has a thin membrane to provide a short path.

A good exchange surface has a thin membrane to provide a short diffusion path.

The diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane .

In which direction does water move during osmosis?

From a dilute solution (high water concentration) to a more concentrated solution (low water concentration).

Osmosis is the movement of across a partially permeable membrane.

Osmosis is the movement of water across a partially permeable membrane.

A piece of plant tissue gains mass in a solution. What does this tell you?

Water has moved into the tissue by osmosis. The surrounding solution is more dilute than the cell contents.

A piece of plant tissue loses mass in a solution. What does this tell you?

Water has moved out of the tissue by osmosis. The surrounding solution is more concentrated than the cell contents.

Why might a piece of plant tissue show no change in mass?

There is no net movement of water – the solution and the cell contents are at the same concentration .

True or False? Osmosis requires energy from respiration.

False. Osmosis is a passive process and does not require energy.

What is the aim of the osmosis required practical?

To investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue .

Outline the method for the osmosis required practical.

Cut equal-sized potato cylinders and measure their starting mass Place each in a different concentration of sugar/salt solution for the same time Remove, dry and reweigh each cylinder

Identify the independent, dependent and two control variables in the osmosis practical.

Independent: concentration of the solution Dependent: percentage change in mass Controls: temperature , time , volume of solution

How do you calculate the percentage change in mass of a potato cylinder?

(final mass − initial mass) ÷ initial mass × 100

Why is the percentage change in mass calculated, rather than just the change in mass?

The cylinders do not all start with exactly the same mass, so using percentage change allows a fair comparison .

On a graph of percentage change in mass against concentration, what does the point where the line crosses zero represent?

The concentration where there is no net movement of water – this equals the concentration inside the potato cells .

In the osmosis required practical, the independent variable is the of the sugar or salt solution.

In the osmosis required practical, the independent variable is the concentration of the sugar or salt solution.

The movement of substances from a dilute to a more concentrated solution (against the concentration gradient), using energy released by respiration.

How does active transport differ from diffusion?

Active transport moves substances against the concentration gradient and requires energy . Diffusion moves substances down the gradient and is passive .

Active transport requires energy released by .

Active transport requires energy released by respiration .

Give an example of active transport in plants .

Root hair cells absorb mineral ions from the very dilute solution in the soil into the cell, where they are more concentrated.

Give an example of active transport in animals .

Glucose (sugar) is absorbed from the gut into the blood, even when the blood already has a higher sugar concentration.

Why do plants need to absorb mineral ions such as magnesium and nitrate?

Magnesium ions are needed to make chlorophyll. Nitrate ions are needed to make amino acids for proteins and growth.

Which of diffusion, osmosis and active transport require energy?

Only active transport requires energy. Diffusion and osmosis are passive.

Compare the direction of movement in diffusion/osmosis and active transport.

Diffusion and osmosis move substances down a concentration gradient. Active transport moves substances against the gradient.

How is osmosis different from diffusion?

Osmosis is the movement of water only , across a partially permeable membrane. Diffusion can be any dissolved particle or gas.

What three things do sports drinks replace that are lost during exercise?

Water Ions (salts) Glucose (sugar)

Why do sports drinks contain glucose?

Glucose is used in respiration to release energy for muscle contraction, replacing the glucose used up during exercise.

If the blood has too little water, cells lose water by osmosis and .

If the blood has too little water, cells lose water by osmosis and shrink .

What is the difference between an isotonic and a hypotonic sports drink?

Isotonic: similar salt and sugar concentration to blood – used for hydration. Hypotonic: lower concentration than blood – used for rapid rehydration.

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Transport in Cells (AQA GCSE Combined Science: Trilogy: Biology): Flashcards

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Name the three processes by which substances are transported into and out of cells.

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Name the three processes by which substances are transported into and out of cells.
Diffusion
Osmosis
Active transport
Diffusion
The net movement of particles of a gas or a dissolved substance from an area of higher concentration to an area of lower concentration.
Is diffusion an active or a passive process?
Passive – it does not require energy from the cell; particles move using their own kinetic energy.
Why is the cell membrane described as partially permeable?
It lets some substances diffuse through but not others.
For example, oxygen and carbon dioxide can pass through, but large molecules such as starch cannot.
Give two substances that diffuse into cells and say why.
Oxygen – needed for aerobic respiration
Carbon dioxide – needed by plant cells for photosynthesis
Give two waste substances that diffuse out of cells.
Urea (from the breakdown of amino acids)
Carbon dioxide (from aerobic respiration)
In diffusion, there is a net movement of particles from a region of higher concentration to a region of concentration.
In diffusion, there is a net movement of particles from a region of higher concentration to a region of lower concentration.
What three factors affect the rate of diffusion?
The concentration gradient (difference in concentrations)
The temperature
The surface area of the membrane
How does a steeper concentration gradient affect the rate of diffusion?
The greater the difference in concentration, the faster the rate of diffusion.
How does increasing the temperature affect the rate of diffusion?
The rate increases, because particles gain more kinetic energy and move faster.
How does a larger surface area affect the rate of diffusion?
A larger surface area gives a faster rate of diffusion.
Why is a single-celled organism's surface area to volume ratio described as large?
Its surface area is large compared with its small volume, so substances only travel a short distance – diffusion alone is enough to meet its needs.
As an organism gets larger, its surface area to volume ratio .
As an organism gets larger, its surface area to volume ratio decreases.
Calculate the surface area to volume ratio of a cube with sides of 2 cm.
Surface area = 6 × (2 × 2) = 24 cm²
Volume = 2 × 2 × 2 = 8 cm³
Ratio = 24 : 8 = 3 : 1
Why do large organisms need exchange surfaces and transport systems?
They have a small surface area to volume ratio, so diffusion alone is too slow to supply all their cells.
Why can't multicellular organisms rely on diffusion across their outer surface alone?
They have a small surface area to volume ratio and a large diffusion distance, so diffusion alone cannot supply substances fast enough for all their cells.
What features make an exchange surface efficient?
A large surface area
A thin membrane (short diffusion path)
A good blood supply (in animals)
Being ventilated (for gas exchange in animals)
How is the small intestine adapted for exchange?
Villi give a large surface area
Wall only one cell thick – short diffusion distance
Good blood supply maintains the concentration gradient
How are the alveoli in the lungs adapted for gas exchange?
Millions of alveoli give a large surface area
Walls one cell thick and moist – short diffusion path
Good blood supply and ventilation maintain the concentration gradient
How are fish gills adapted for gas exchange?
Many filaments and lamellae give a large surface area
Good blood supply maintains the concentration gradient
How are plant roots and leaves adapted for exchanging materials?
Roots: branched, with root hair cells that increase surface area for absorbing water and mineral ions
Leaves: stomata and air spaces allow gases to diffuse in and out over a short distance
A good exchange surface has a thin membrane to provide a short path.
A good exchange surface has a thin membrane to provide a short diffusion path.
Osmosis
The diffusion of water from a dilute solution to a more concentrated solution through a partially permeable membrane.
In which direction does water move during osmosis?
From a dilute solution (high water concentration) to a more concentrated solution (low water concentration).
Osmosis is the movement of across a partially permeable membrane.
Osmosis is the movement of water across a partially permeable membrane.
A piece of plant tissue gains mass in a solution. What does this tell you?
Water has moved into the tissue by osmosis.
The surrounding solution is more dilute than the cell contents.
A piece of plant tissue loses mass in a solution. What does this tell you?
Water has moved out of the tissue by osmosis.
The surrounding solution is more concentrated than the cell contents.
Why might a piece of plant tissue show no change in mass?
There is no net movement of water – the solution and the cell contents are at the same concentration.
True or False?
Osmosis requires energy from respiration.
False.
Osmosis is a passive process and does not require energy.
What is the aim of the osmosis required practical?
To investigate the effect of a range of concentrations of salt or sugar solutions on the mass of plant tissue.
Outline the method for the osmosis required practical.
Cut equal-sized potato cylinders and measure their starting mass
Place each in a different concentration of sugar/salt solution for the same time
Remove, dry and reweigh each cylinder
Identify the independent, dependent and two control variables in the osmosis practical.
Independent: concentration of the solution
Dependent: percentage change in mass
Controls: temperature, time, volume of solution
How do you calculate the percentage change in mass of a potato cylinder?
(final mass − initial mass) ÷ initial mass × 100
Why is the percentage change in mass calculated, rather than just the change in mass?
The cylinders do not all start with exactly the same mass, so using percentage change allows a fair comparison.
On a graph of percentage change in mass against concentration, what does the point where the line crosses zero represent?
The concentration where there is no net movement of water – this equals the concentration inside the potato cells.
In the osmosis required practical, the independent variable is the of the sugar or salt solution.
In the osmosis required practical, the independent variable is the concentration of the sugar or salt solution.
Active transport
The movement of substances from a dilute to a more concentrated solution (against the concentration gradient), using energy released by respiration.
How does active transport differ from diffusion?
Active transport moves substances against the concentration gradient and requires energy.
Diffusion moves substances down the gradient and is passive.
Active transport requires energy released by .
Active transport requires energy released by respiration.
Give an example of active transport in plants.
Root hair cells absorb mineral ions from the very dilute solution in the soil into the cell, where they are more concentrated.
Give an example of active transport in animals.
Glucose (sugar) is absorbed from the gut into the blood, even when the blood already has a higher sugar concentration.
Why do plants need to absorb mineral ions such as magnesium and nitrate?
Magnesium ions are needed to make chlorophyll.
Nitrate ions are needed to make amino acids for proteins and growth.
Which of diffusion, osmosis and active transport require energy?
Only active transport requires energy.
Diffusion and osmosis are passive.
Compare the direction of movement in diffusion/osmosis and active transport.
Diffusion and osmosis move substances down a concentration gradient.
Active transport moves substances against the gradient.
How is osmosis different from diffusion?
Osmosis is the movement of water only, across a partially permeable membrane.
Diffusion can be any dissolved particle or gas.
What three things do sports drinks replace that are lost during exercise?
Water
Ions (salts)
Glucose (sugar)
Why do sports drinks contain glucose?
Glucose is used in respiration to release energy for muscle contraction, replacing the glucose used up during exercise.
If the blood has too little water, cells lose water by osmosis and .
If the blood has too little water, cells lose water by osmosis and shrink.
What is the difference between an isotonic and a hypotonic sports drink?
Isotonic: similar salt and sugar concentration to blood – used for hydration.
Hypotonic: lower concentration than blood – used for rapid rehydration.

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