IGCSE Biology 0654 B3 and B4

Describe the term diffusion

the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down concentration gradient), as a result of their random movement

Define the term osmosis

• The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane.

• It is a passive process as no energy is required

Through where does water diffuse and how?

Through partially permeable membranes by osmosis

Define water potential.

A measure of how freely water molecules can move;

• dilute solutions have high water potential

• concentrated solutions have low water potential.

Describe what happens to a plant cell in a dilute solution.

Water enters the cell by osmosis

Vacuole expands

Turgor pressure increases

Cell becomes turgid.

Describe what happens to a plant cell in a concentrated solution.

1) Water leaves the cell by osmosis

2) Vacuole shrinks

3) Turgor pressure decreases

4) Cell becomes flaccid.

5) Continued water loss leads to plasmolysis.

Describe what happens to a plant cell in a solution with equal water potential.

No net movement of water by osmosis

Volume and shape of the cell remain unchanged.

Define the term turgid.

Cell has absorbed water by osmosis

Causing the vacuole to expand and press against the cell wall, making the cell firm.

Define the term flaccid.

Has lost water by osmosis

Causing:

• Vacuole to shrink

• The cell to become soft and limp.

Define the term turgor pressure.

Pressure exerted by water inside the vacuole against the cytoplasm and the cell wall.

Define the term plasmolysis.

When too much water leaves the plant cell by osmosis, causing the cell membrane to pull away from the cell wall.

Investigate the effect of immersing plant tissue in solutions of different concentrations.

• Place identical plant tissue samples in solutions of different concentrations.

• In dilute solutions: cells become turgid;

• In concentrated solutions, cells become flaccid or plasmolysed

• In equal concentrations, cells show no change.

Explain the importance of water potential and osmosis in the uptake and loss of water by organisms.

Osmosis controls the movement of water into and out of cells.

If cells gain or lose too much water, they may burst or shrink.

Maintaining equal water potential with the surrounding solution prevents damage and keeps cells functioning properly.

Describe what happens to an animal cell in a concentrated solution.

• The solution has a lower water potential than inside the cell

• so water moves out of the cell by osmosis.

• The cell shrinks.

Describe what happens to an animal cell in a dilute solution.(SOS)

• Solution has higher water potential than inside the cell,

• so water enters the cell by osmosis.

• The cell swells and may burst.

State one reason why plant cells are less likely to burst in dilute solutions compared to animal cells.

Plant cells have a cell wall, which provides structural support and prevents them from bursting when water enters by osmosis.

Describe the term active transport

• Movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration.

• It is an active process as energy (from respiration) is required to move particles against a concentration gradient across the membrane (opposite direction of diffusion and osmosis)

Explain the importance of active transport in organisms.

• Allows cells to move substances against the concentration gradient, using energy from respiration.

• This is essential for absorbing nutrients when they are in lower concentration outside the cell.

Explain the importance of active transport in ion uptake by root hair cells.

• Enables root hair cells to absorb mineral ions from the soil even when their concentration is lower in the soil than in the cell.

• This is essential for plant growth and development.

Describe how root hair cells are adapted for active transport.

Root hair cells have:

– A large surface area to increase absorption of mineral ions by active transport and water by osmosis

– Many mitochondria to provide energy for active transport

State two substances absorbed by root hair cells and how they are taken up.

– Mineral ions: by active transport
– Water: by osmosis

List the chemical elements that make up carbohydrates, fats and proteins

Carbohydrates and fats (lipids): Carbon, hydrogen, oxygen (CAR IN OHIO)
Proteins: Carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorous (CAR IN OHIO NISUPHO)

State what polymers are made from.

Polymers (large molecules) are made from monomers (smaller molecules)

State the monomer and polymer for carbohydrates.

Monomer—> glucose.

Polymers —> starch, cellulose, and glycogen (all carbohydrates).

State the monomers that form lipids.

Lipids are formed when fatty acids and glycerol join together.

State the monomer and polymer for proteins.

The monomers are amino acids, which join together to form proteins.

Describe the relationship between monomers and polymers in biological molecules.

Monomers —> small molecules that join together to form larger molecules (polymers)

Describe the chemical tests that are used to detect the presence of biological molecules in Iodine Solution (Starch)

Add a few drops of iodine solution to the test solution /food sample.

Starch = colour will change from orange-brown to blue-black

Describe the chemical tests that are used to detect the presence of biological molecules in Benedict’s solution (Sugars (glucose and fructose)

In a test tube, add the equal volume of Benedict’s reagent to the test solution.
Heat in a water bath at 60°C for 5 mns

Depending on the amount of sugar = from blue to green, to yellow, to orange and to red

Describe the chemical tests that are used to detect the presence of biological molecules in Biuret solution (Proteins)

Add drops of Biuret reagent to the food sample

Proteins = colour will change from blue to purple

Describe the chemical tests that are used to detect the presence of biological molecules in Ethanol (fats and oils)

Mix the food sample with ethanol in a test tube until the fat dissolves.
Add a few millimeters of water.

Fat and oil = milky white emulsion will form

Describe the importance of diffusion of gases and solutes in living organisms (RENEWABLE!)

Important for:

• respiration

• nutrient uptake

• waste removal in living organisms.

Describe how O2 and C02 are exchanged in the lungs.

Oxygen diffuses from the alveoli into the blood

Carbon dioxide diffuses from the blood into the alveoli to be exhaled.

Describe the role of diffusion of gases in leaves.

02 and C02 diffuse in and out of leaves through stomata for photosynthesis and respiration.

State four factors that affect the rate of diffusion.

• Surface area

• Temperature

• Concentration gradient

• Distance

Describe how surface area affects the rate of diffusion.

Larger surface area increases the rate of diffusion because more particles can pass through at once.

Describe how temperature affects the rate of diffusion.

A higher temperature increases the rate of diffusion because particles have more kinetic energy and move faster.

Describe how concentration gradient affects the rate of diffusion.

A steeper concentration gradient increases the rate of diffusion because the greater the difference in concentration, the faster the movement.

Describe how distance affects the rate of diffusion.

A shorter distance increases the rate of diffusion because particles take less time to pass through.