Biology Paper 1 – Triple Higher Combined (Lecture Review)

70 question–answer flashcards covering key concepts from the Biology Paper 1 (Triple Higher Combined) lecture notes.

Name three organelles found in plant but not animal cells.

Cell wall, chloroplasts, and a large permanent vacuole.

What is the main function of mitochondria?

They are the site of aerobic respiration and generate ATP (energy) for the cell.

What is the function of chloroplasts?

They carry out photosynthesis by absorbing light energy to convert CO₂ and H₂O into glucose and O₂.

Which part of a leaf cell is most transparent?

The upper epidermis, allowing light to pass to photosynthetic cells beneath.

Give one reason a student might see no cells under a microscope.

The slide may be upside-down/out of focus, so the sample is not in the focal plane or insufficiently illuminated.

Why use a very thin layer of onion epidermis on a slide?

It is only one cell thick, so light passes through easily and individual cell structures are visible.

Why is a cover slip lowered at an angle onto the slide?

To push out air and avoid trapping bubbles that would obstruct the view of the specimen.

Why do we add iodine solution to onion cells?

Iodine stains the cytoplasm/nucleus, increasing contrast so structures are easier to see.

Name two pieces of equipment used to prepare cells for light microscopy.

A scalpel (or forceps) and a glass slide/cover slip.

State two differences you would notice in onion cells under an electron microscope.

Far more detail is visible – individual mitochondria and ribosomes can be seen, and images appear black-and-white/greyscale rather than coloured.

What is the function of the palisade mesophyll layer?

It is the main site of photosynthesis in a leaf.

Which part of a leaf allows gas exchange?

Stomata (mainly on the lower epidermis).

Name the cells that control water loss from a leaf.

Guard cells (they open and close the stomata).

What is the function of the waxy cuticle on a leaf?

It forms a waterproof layer to reduce evaporation and water loss.

What is the scientific term for the overall movement of water through a plant?

Transpiration (or the transpiration stream).

Which change in leaf conditions decreases water loss?

Closing the stomata (e.g., by guard-cell turgor changes).

Briefly compare the structure and function of xylem and phloem.

Xylem consists of dead, lignified, hollow vessels that carry water/mineral ions one way (roots → leaves). Phloem is made of living sieve tubes with companion cells and transports sugars (sucrose) both up and down the plant (translocation).

Which mesophyll structure is absent from a root hair cell?

Chloroplasts.

Name three aseptic techniques used in microbiology practicals.

Disinfect the bench, flame the inoculating loop, and keep the Petri-dish lid closed except when transferring cultures.

Describe two aseptic techniques specific to the agar plate practical.

(1) Flame the neck of culture bottles before and after use. (2) Secure the Petri-dish lid with tape and incubate inverted to prevent condensation contamination.

Why must the inoculating loop be sterilised before use?

To kill any unwanted microorganisms and prevent contamination of the culture.

Why are cultures in schools not incubated above 25 °C?

Higher temperatures could encourage growth of pathogenic bacteria that thrive nearer human body temperature (37 °C).

Outline the osmosis potato cylinder method.

Cut equal potato cylinders, record initial mass, place each in different sucrose solutions for a set time, blot, re-weigh, and calculate percentage mass change to determine water movement.

Describe the effect of pH on amylase activity.

Amylase works fastest at its optimum pH (~7); extremes of pH denature the enzyme, slowing starch breakdown.

Give two control variables for the amylase temperature practical.

Keep substrate (starch) concentration and pH constant (or keep enzyme concentration/volume constant).

Why leave separate starch and amylase solutions for 5 min before mixing?

To allow them to reach the required test temperature (thermal equilibration).

How could you extend/improve the amylase experiment?

Test additional temperatures or pH values, take replicates for each condition, or use a colorimeter to obtain quantitative results.

Which chemical is used to test for protein?

Biuret solution (sodium hydroxide plus copper(II) sulfate), which turns lilac/purple if protein is present.

What chemical is used to test for starch?

Iodine solution, which turns blue-black in the presence of starch.

What reagent is used to test for reducing sugar?

Benedict’s solution; after heating it changes from blue to brick-red/orange if reducing sugar is present.

Amylase is a polymer. What are its monomers?

Amino acids.

Where is protein digested in the human body?

In the stomach and the small intestine (by enzymes such as pepsin, trypsin, and peptidases).

Name three organs/tissues that produce amylase.

Salivary glands, pancreas, and the small-intestinal wall.

What does the gall bladder do?

Stores and concentrates bile, releasing it into the small intestine when needed.

Why would a blocked bile duct impair fat digestion?

Bile cannot reach the intestine to emulsify fats; reduced surface area for lipase lowers the rate of fat breakdown and absorption, leading to greasy stools and nutrient loss.

Explain, using the lock-and-key model, how amylase breaks down starch.

Starch (substrate) fits into amylase’s active site, forming an enzyme-substrate complex. Bonds in starch are hydrolysed, producing maltose; the unchanged enzyme is free to catalyse more reactions.

Write the balanced chemical equation for aerobic respiration.

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O (+ ATP energy).

In which organelle does aerobic respiration occur?

Mitochondria.

Give two uses of the energy released by respiration.

Muscle contraction and active transport (also maintaining body temperature, cell division, etc.).

Give three key differences between aerobic and anaerobic respiration in humans.

Aerobic uses oxygen, produces CO₂ & H₂O and lots of ATP; anaerobic needs no oxygen, makes lactic acid and far less ATP, leading to an oxygen debt.

Why can’t a person with blood group A receive group B blood?

Group A blood contains anti-B antibodies that would bind B antigens on donor RBCs, causing agglutination and potentially fatal transfusion reactions.

Why is blood group O called the universal donor?

Its red cells lack both A and B antigens, so they are not attacked by anti-A or anti-B antibodies in any recipient’s plasma.

Which cell structure contains most of the cell’s DNA?

The nucleus (in chromosomes).

What does a gene code for?

A specific protein (or polypeptide).

What happens when a tumour forms in tissue?

Cells divide uncontrollably, producing a mass of abnormal cells that may disrupt normal function.

From an imaging scan, how could you tell a tumour is malignant?

It has irregular edges, invades neighbouring tissues, and/or shows evidence of metastasis via blood or lymph vessels.

State symptoms that could arise from low levels of red cells, white cells, and platelets.

Low red cells → fatigue/pallor; low white cells → frequent infections; low platelets → easy bruising/bleeding.

How does mitosis produce genetically identical daughter cells?

DNA replicates, chromosomes align on the equator, sister chromatids separate evenly, and cytokinesis splits the cytoplasm, so each new cell receives identical chromosomes.

Name the process by which stem cells become specialised.

Differentiation.

How are monoclonal antibodies produced?

Mouse is immunised with antigen, spleen B cells are fused with myeloma cells to form hybridomas, which are screened and cloned to secrete identical (monoclonal) antibodies.

How can monoclonal antibodies be used to treat HIV?

They are engineered to bind specific HIV envelope proteins, neutralising the virus or marking infected cells for immune destruction.

How do vaccines protect against HIV (or any virus)?

They introduce harmless antigens that trigger antibody and memory-cell production, so the immune system responds rapidly on real exposure.

Why do antibodies bind specifically to antigens?

The variable region of an antibody has a complementary shape to the antigen’s epitope, allowing highly specific binding.

Give two adaptations of a nerve cell and their advantages.

Long axon transmits impulses over distance; myelin sheath insulates, speeding up conduction; branched dendrites connect to many other neurons.

Give two adaptations of a root hair cell and their advantages.

Long, thin projection greatly increases surface area for water/mineral uptake; thin cell wall and large vacuole lower water potential to aid osmosis.

Give two adaptations of a muscle cell and their advantages.

Contains many mitochondria for ATP supply; long fibres with actin and myosin allow contraction and movement.

Give two adaptations of a sperm cell and their advantages.

Flagellum for motility toward the egg; many mitochondria supply energy; acrosome contains enzymes to penetrate the egg’s membrane.

Calculate the surface-area-to-volume ratio of a cube measuring 2 cm × 2 cm × 2 cm.

Surface area = 6 × (2 cm × 2 cm) = 24 cm²; volume = 8 cm³; SA:Vol ratio = 24 : 8 = 3 : 1.

How does SA:Vol ratio change as organisms get larger?

The SA:Vol ratio decreases, so exchange becomes less efficient and specialised systems are needed.

List key adaptations of alveoli and intestinal villi for exchange.

Large surface area (folds, microvilli), one-cell-thick walls for short diffusion distance, moist surfaces, and an extensive blood capillary network to maintain steep concentration gradients.

Write the balanced equation for photosynthesis.

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂ (light energy & chlorophyll).

Name a living plant cell that lacks chloroplasts.

A root hair cell (also xylem vessels or most root epidermal cells).

Give two ways plants defend against pathogens.

Physical barriers (cell walls, tough bark, waxy cuticle) and chemical defences (antimicrobial compounds, poisons, enzymes).

What is the function of stomata?

They open and close to allow gas exchange (CO₂ in, O₂ and water vapour out).

Name one fungal disease of plants or humans.

Rose black spot (plant) or athlete’s foot (human).

How is HIV commonly transmitted?

Through unprotected sexual intercourse, infected blood/needle sharing, or from mother to baby during birth or breastfeeding.

How does mimicry help the hornet moth survive?

It resembles a stinging hornet, so predators avoid it, reducing chances of being eaten.

List the major parts you would label on a heart diagram.

Aorta, vena cava, pulmonary artery, pulmonary vein, left/right atria, left/right ventricles, tricuspid and bicuspid valves, septum.

Explain the roles of a pacemaker, a heart valve, and a stent.

Pacemaker: device sending electrical impulses to regulate heartbeat; Valve: prevents back-flow, ensuring one-way blood flow; Stent: mesh tube inserted into an artery to keep it open and maintain blood flow.

Differentiate between the transpiration stream and translocation.

Transpiration stream is the one-way movement of water/mineral ions up xylem driven by evaporation at leaves; translocation is the two-way movement of sugars and other solutes through phloem from sources to sinks.