Biology Paper 1

Topic 1: Cell Biology

Cell structure

Animal cells

  • Nucleus → contains genetic material/DNA

  • Cytoplasm → where chemical reactions happen

  • Cell membrane → controls movement of substances in/out

  • Mitochondria → aerobic respiration

  • Ribosomes → protein synthesis

Plant cells also have:

  • Cell wall → strengthens/supports cell

  • Chloroplasts → photosynthesis

  • Permanent vacuole → contains cell sap

Prokaryotes

  • Smaller and simpler than eukaryotic cells

  • No nucleus

  • DNA is a single circular loop

  • May contain plasmids

  • Example: bacteria

Microscopy

Magnification = image size ÷ actual size

Remember:

  • 1 mm = 1000 μm

  • 1 μm = 1000 nm

Cell differentiation

  • Cells become specialised for a particular function.

  • In animals, most differentiation happens early in development.

  • Plant cells retain the ability to differentiate throughout their lives.

Stem cells

Stem cells can:

  • Self-renew

  • Differentiate into different cell types

Embryonic stem cells can form many different cell types.

Adult stem cells have more limited differentiation.

Mitosis

Used for:

  • Growth

  • Repair

  • Replacement of damaged cells

  • Asexual reproduction

Sequence:
Cell grows → DNA replicated → chromosomes separated → nucleus divides → cytoplasm divides

Produces 2 genetically identical diploid cells (daughter cells)

Transport

Diffusion

  • Movement of particles from high → low concentration

  • Does not require energy

Osmosis

  • Movement of water molecules

  • Through a partially permeable membrane

  • From a dilute solution → concentrated solution

Active transport

  • Moves substances from low → high concentration

  • Requires energy from respiration

  • Important for absorbing mineral ions in plants and glucose in the small intestine.


Topic 2: Organisation

Levels of organisation

Cells → tissues → organs → organ systems → organism

Digestive system

Amylase

  • Starch → sugars

  • Produced by salivary glands, pancreas and small intestine

Protease

  • Proteins → amino acids

  • Produced by stomach, pancreas and small intestine

Lipase

  • Lipids → fatty acids + glycerol

  • Produced by pancreas and small intestine

Bile

Produced by the liver, stored in the gall bladder.

Functions:

  • Neutralises stomach acid

  • Emulsifies fats → increases surface area for lipase


Heart and blood

Heart pathway

Vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta

Remember:

  • Right side → pumps blood to lungs

  • Left side → pumps blood around body

  • Left ventricle has a thicker muscular wall.

Blood vessels

Arteries

  • Carry blood away from heart

  • Thick muscular/elastic walls

  • Small lumen

  • High pressure

Veins

  • Carry blood towards heart

  • Thinner walls

  • Large lumen

  • Valves prevent backflow

Capillaries

  • Very narrow

  • Walls one cell thick

  • Allow exchange of substances

Blood

Red blood cells

  • Carry oxygen using haemoglobin

  • Biconcave shape

  • No nucleus → more space for haemoglobin

White blood cells

  • Defend against pathogens

Platelets

  • Help blood clot

Plasma

  • Transports cells and dissolved substances.


Topic 3: Infection and Response

Pathogens

Four main types:

Bacteria

  • Living cells

  • Can produce toxins

  • Antibiotics can kill bacteria

Viruses

  • Much smaller than bacteria

  • Reproduce inside living cells

  • Can damage/destroy cells

  • Antibiotics do not work against viruses

Fungi

  • Can cause diseases such as athlete’s foot

Protists

  • Mostly single-celled

  • Some cause disease, e.g. malaria


Human defence system

Physical barriers

  • Skin → physical barrier

  • Mucus → traps pathogens

  • Cilia → move mucus towards throat

  • Stomach acid → kills pathogens

White blood cells

They:

  1. Engulf pathogens by phagocytosis

  2. Produce antibodies

  3. Produce antitoxins

Vaccination

A vaccine introduces a harmless form of a pathogen’s antigen.

This causes:

  • White blood cells to produce antibodies

  • Memory cells to remain

If the pathogen enters again:

  • Memory cells produce antibodies rapidly

  • You are protected from the disease or experience less severe symptoms.

Antibiotics

  • Kill bacteria

  • Do not kill viruses

  • Overuse can cause antibiotic resistance.


Plant diseases

Plants can be infected by:

  • Fungi

  • Bacteria

  • Viruses

  • Insects

Signs include:

  • Stunted growth

  • Discoloured leaves

  • Spots

  • Decay

Plants defend themselves using:

  • Cellulose cell walls

  • Tough waxy cuticle

  • Chemicals

  • Antimicrobial substances


Topic 4: Bioenergetics

Photosynthesis

Word equation:

Carbon dioxide + water → glucose + oxygen

Requires:

  • Light

  • Chlorophyll

Symbol equation:

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Limiting factors

  • Light intensity

  • Carbon dioxide concentration

  • Temperature

At first, increasing a limiting factor increases the rate. Eventually another factor becomes limiting.

Uses of glucose

Plants use glucose for:

  • Respiration

  • Making cellulose

  • Making starch for storage

  • Making fats/oils

  • Making amino acids


Respiration

Aerobic respiration

Glucose + oxygen → carbon dioxide + water + energy

Occurs mainly in mitochondria.

Energy released is used for:

  • Movement

  • Keeping warm

  • Building larger molecules

  • Active transport

Anaerobic respiration

In animals

Glucose → lactic acid

Produces less energy than aerobic respiration.

Lactic acid builds up during vigorous exercise and causes oxygen debt.

In yeast

Glucose → ethanol + carbon dioxide

This is fermentation and is useful in:

  • Bread making

  • Alcohol production


Exercise

During exercise:

  • Muscles need more energy

  • Rate of respiration increases

  • Heart rate increases

  • Breathing rate and depth increase

Oxygen debt

After vigorous exercise, extra oxygen is needed to:

  • Break down/remove lactic acid

  • Restore normal conditions



Required practicals for Paper 1

1. Microscopy

Question: Describe how to prepare and observe a specimen using a light microscope.

  1. Cut a thin section of the specimen.

  2. Place the specimen on a glass slide.

  3. Add a drop of stain to make structures easier to see.

  4. Carefully place a coverslip over the specimen using a mounted needle.

  5. Place the slide on the microscope stage.

  6. Start with the lowest-power objective lens.

  7. Use the coarse focusing knob to bring the specimen into focus.

  8. Use the fine focusing knob to obtain a clear image.

  9. Increase the magnification if necessary and refocus.

  10. Draw what you observe using clear lines, with no shading, and add labels.

Exam points: Thin specimen = light can pass through. Stain = improves contrast.


2. Osmosis in Potato

Question: Describe an investigation into the effect of solution concentration on osmosis in potato tissue.

  1. Prepare several solutions with different concentrations.

  2. Cut potato cylinders to the same length and diameter.

  3. Measure and record the initial mass of each potato cylinder.

  4. Place each cylinder into a different concentration of solution.

  5. Keep the volume of solution, temperature and time the same.

  6. Leave the potato cylinders for a set period.

  7. Remove them and carefully blot them dry.

  8. Measure and record their final masses.

  9. Calculate the percentage change in mass:

Percentage change = (change in mass ÷ initial mass) × 100

  1. Repeat the experiment and calculate a mean.

  2. Plot concentration against percentage change in mass.

Exam points:

  • Water moves through a partially permeable membrane.

  • Water moves from a more dilute solution to a more concentrated solution.

  • No net movement occurs at the concentration where the percentage change is 0%.

Control variables: temperature, time, potato size, volume of solution.


3. Food Tests

Starch

Question: Describe the test for starch.

  1. Place the food sample in a test tube.

  2. Add iodine solution.

  3. If starch is present, the solution turns blue-black.

  4. If starch is absent, it remains orange-brown.

Reducing sugars

  1. Add Benedict’s solution to the food sample.

  2. Place the test tube in a hot water bath.

  3. Heat for several minutes.

  4. A positive result produces a colour change from blue towards green/yellow/orange/brick-red, depending on concentration.

  5. A negative result remains blue.

Protein

  1. Add Biuret solution to the food sample.

  2. A positive result turns lilac/purple.

  3. A negative result remains blue.

Lipids

  1. Add ethanol to the food sample and shake.

  2. Add water.

  3. A positive result produces a cloudy white emulsion.

  4. A negative result remains clear.


4. Enzymes — Effect of pH

Question: Describe how to investigate the effect of pH on amylase activity.

  1. Prepare test tubes containing buffer solutions of different pH values.

  2. Add the same volume and concentration of amylase to each.

  3. Add the same volume and concentration of starch to each.

  4. Keep the temperature constant using a water bath.

  5. Start the stopwatch when the starch is added.

  6. At regular intervals, place a drop of the mixture onto iodine solution on a spotting tile.

  7. Continue until the iodine remains orange-brown, showing that no starch remains.

  8. Record the time taken.

  9. Repeat each pH value and calculate a mean.

  10. Calculate the rate:

Rate = 1 ÷ time

  1. Plot pH against rate of reaction.

Why iodine? It tests whether starch remains.

Control variables: temperature, enzyme concentration, starch concentration, volumes and time intervals.


5. Photosynthesis — Light Intensity

Question: Describe an investigation into the effect of light intensity on the rate of photosynthesis.

  1. Place a piece of pondweed in a beaker of sodium hydrogencarbonate solution.

  2. Position a lamp at a measured distance from the pondweed.

  3. Allow the pondweed to equilibrate.

  4. Turn on the lamp and measure the number of oxygen bubbles produced in a set time.

  5. Repeat at different distances from the lamp.

  6. Keep the temperature constant, for example using a heat shield/water bath.

  7. Repeat each measurement and calculate a mean.

  8. Calculate the rate of photosynthesis, such as:

Rate = number of bubbles ÷ time

  1. Plot light intensity/distance against rate of photosynthesis.

Important: Counting bubbles is only an estimate because bubble size can vary. Measuring the volume of oxygen produced would be more accurate.

Control variables: temperature, carbon dioxide concentration, pondweed species/length and time.


6. Antibiotics/Antiseptics — Effect on Bacterial Growth

Question: Describe how to investigate the effect of an antibiotic on bacterial growth.

  1. Spread bacteria evenly across an agar plate using an aseptic technique.

  2. Place paper discs containing different antibiotics onto the agar.

  3. Place the lid on the Petri dish.

  4. Incubate the plate at an appropriate temperature.

  5. Observe the clear zones of inhibition around the discs.

  6. Measure the diameter of each clear zone.

  7. Repeat the experiment and calculate a mean.

  8. Compare the sizes of the zones to determine which antibiotic was most effective.

Aseptic technique

To reduce contamination:

  • Sterilise equipment.

  • Use a sterile Petri dish and agar.

  • Keep the lid closed as much as possible.

  • Sterilise the inoculating equipment.

  • Do not incubate cultures at human body temperature in a school laboratory.

Exam point: A larger zone of inhibition generally indicates that the antibiotic was more effective against that bacterium.