Diffusion
Osmosis
Active Transport
Biological Molecules
Food Tests
100
What is meant by diffusion?
A. Movement of particles from low to high concentration using energy
B. Net movement of particles from high to low concentration due to random movement
C. Movement of water only through a membrane
D. Movement of particles from high to low concentration using energy
B. Net movement of particles from high to low concentration due to random movement
100
What is osmosis?
A. Movement of any particles from high to low concentration
B. Movement of water from low to high water potential
C. Net movement of water molecules from higher water potential to lower water potential through a partially permeable membrane
D. Movement of water using energy
C. Net movement of water molecules from higher water potential to lower water potential through a partially permeable membrane
100
What is active transport?
A. Movement of particles from high to low concentration without energy
B. Movement of particles from low to high concentration using energy from respiration
C. Movement of water through a partially permeable membrane
D. Movement of particles from high to low concentration using energy
B. Movement of particles from low to high concentration using energy from respiration
100
State the main elements found in carbohydrates.
Carbon, Hydrogen, Oxygen
100
Describe how you would test a food sample for starch.
Add a few drops of iodine solution to the food sample
A positive result is a colour change from brown/orange to blue-black
200
State the structure that substances must pass through when entering or leaving a cell by diffusion.
Name one substance that moves into cells by diffusion in humans.
Cell membrane
Oxygen / Carbon Dioxide
200
State how water enters and leaves cells.
Water moves into and out of cells by osmosis through the cell membrane.
200
State two features of active transport.
Movement of particles from a region of lower concentration to a region of higher concentration (against the concentration gradient).
Requires energy (from respiration).
200
State the small molecules that join together to form fats and oils.
Fatty acids
Glycerol
200
Describe how you would test a food sample for fats and oils.
Add ethanol to the food sample and shake
Add water
A positive result is a white/milky emulsion
300
Describe why diffusion of gases and dissolved substances is important in living organisms.
You should include examples in your answer.
Diffusion allows essential substances to enter cells and waste substances to leave.
For example, oxygen diffuses into cells for respiration, carbon dioxide diffuses out, and nutrients such as glucose diffuse into cells.
300
Explain the following terms ;
Plasmolyezed - Flaccid - Turgid
Turgid
Water enters the plant cell by osmosis from a region of higher water potential to lower water potential.
The vacuole swells and pushes the cytoplasm against the cell wall, creating turgor pressure, which makes the cell firm.
Flaccid
There is little or no net movement of water into the cell.
The vacuole is not full, turgor pressure is low, and the cell becomes limp.
Plasmolysed
Water leaves the cell by osmosis to a region of lower water potential.
The vacuole shrinks and the cell membrane pulls away from the cell wall.
300
Explain why active transport is important for cells.
Active transport allows cells to take in substances even when they are in a lower concentration outside the cell than inside.
This enables cells to obtain necessary molecules or ions that they need to function.
300
Name two large carbohydrate molecules made from glucose.
Any two from: starch, glycogen, cellulose
300
Describe how you would test a food sample for protein.
Add Biuret reagent
A positive result is a colour change from blue to purple/lilac
400
Two experiments are set up to investigate diffusion of a gas.
In experiment 1 the temperature is 20°C.
In experiment 2 the temperature is 40°C.
(a) In which experiment will diffusion be faster?
(b) Explain why.
(a) Experiment 2 (40°C).
(b) At a higher temperature, particles have more kinetic energy, so they move faster and spread out more quickly.
400
Explain what happens to a plant cell when it is placed in:
(a) distilled water
(b) a concentrated salt solution
Use the terms turgid, turgor pressure, plasmolysis, flaccid where appropriate.
(a) Water enters the cell by osmosis. The vacuole swells and pushes against the cell wall. The cell becomes turgid and turgor pressure increases.
(b) Water leaves the cell by osmosis. The vacuole shrinks, the cell membrane pulls away from the cell wall, and the cell becomes flaccid. If severe, plasmolysis occurs.
400
Explain how root hair cells take up mineral ions from the soil.
Mineral ions are often at a lower concentration in the soil than inside the root hair cell.
They are absorbed against the concentration gradient by active transport using energy from respiration.
400
State the chemical elements present in proteins
Carbon
Hydrogen
Oxygen
Nitrogen
400
Describe how you would test a food sample for reducing sugars.
Add Benedict’s solution to the food sample
Heat in a water bath
A positive result is a colour change from blue to green/yellow/orange/brick-red (depending on amount of sugar)
500
During exercise, muscle cells use oxygen more rapidly.
Explain how this affects the concentration gradient for oxygen and why the rate of diffusion of oxygen into the cells changes.
Using oxygen lowers its concentration inside the muscle cells.
This makes the difference in concentration between the blood and the cells larger (steeper concentration gradient).
A steeper gradient increases the rate of diffusion, so oxygen enters the cells faster.
500
Why are water potential and osmosis important for water moving in and out of cells?
Osmosis lets water move through cell membranes from high water potential to low water potential.
This helps cells keep their shape, keeps plant cells firm, and lets organisms control their water levels.
Without it, cells could shrink or burst.
500
A cell contains a high concentration of a particular ion. The surrounding solution contains a lower concentration. Explain how the cell could continue to take in more of this ion.
The ion would be moved into the cell by active transport. It would pass through the cell membrane from lower to higher concentration, against the concentration gradient, using energy from respiration.
500
Explain why proteins contain nitrogen but carbohydrates and fats do not.
Proteins are made from amino acids
Amino acids contain nitrogen
Carbohydrates and fats are made from glucose or fatty acids and glycerol, which do not contain nitrogen
500
A student carries out four food tests on the same sample. The results are: iodine stays brown, Benedict’s turns brick-red after heating, Biuret remains blue, and the ethanol test forms a milky emulsion. Identify the nutrients present and absent.
Starch absent
Reducing sugar present
Protein absent
Fat/oil present