Separate Science Biology - Extras for Paper 1

What is aseptic technique and why is it used when culturing microorganisms?

Aseptic technique is a set of procedures used to prevent contamination of a culture by unwanted microorganisms. It ensures that only the intended bacterium grows, and protects the experimenter from harmful microbes.

What steps are taken to maintain aseptic technique when preparing an agar plate?

The inoculating loop is sterilised in a flame before and after use; the agar plate lid is only briefly lifted at an angle; work is done near a Bunsen flame to create an upward air current that keeps microbes away; the plate is sealed with tape (but not all the way round, to allow gas exchange).

Why must agar plates be incubated at 25°C in schools rather than 37°C?

25°C reduces the risk of culturing microorganisms that could be harmful to humans (pathogens grow more readily at 37°C, which is body temperature).

How do you calculate the area of an inhibition zone around an antibiotic disc?

Use the formula: area = π × r² (where r is the radius of the clear zone). The larger the area, the more effective the antibiotic at killing bacteria.

What does a clear inhibition zone around an antibiotic disc on an agar plate tell you?

It shows that the antibiotic has killed or prevented the growth of the bacteria in that area. A larger zone means the antibiotic is more effective against that bacterium.

What is the difference between xylem and phloem in plants?

Xylem carries water and dissolved minerals from roots to leaves (one direction only). Phloem carries dissolved sugars (e.g. sucrose) made by photosynthesis to all parts of the plant that need them (in both directions).

What type of cells make up xylem vessels, and what are their key features?

Xylem vessels are made from dead cells with no end walls, forming a continuous hollow tube. Their walls are strengthened with lignin, making them rigid and waterproof.

What is transpiration?

Transpiration is the loss of water vapour from the leaves of a plant through the stomata (tiny pores, mainly on the underside of leaves) by evaporation and diffusion.

What four factors increase the rate of transpiration, and why?

1. Higher temperature – water evaporates faster. 2. Higher light intensity – stomata open wider for photosynthesis. 3. Lower humidity – greater concentration gradient for water vapour to diffuse out. 4. Higher wind speed – removes water vapour from around the leaf, maintaining the concentration gradient.

What is a potometer and what is it used to measure?

A potometer is a piece of apparatus used to measure the rate of water uptake by a plant shoot (used as an estimate of transpiration rate). A bubble moves along a capillary tube as water is taken up.

What is translocation in plants?

Translocation is the movement of dissolved sugars (sucrose) and other solutes through the phloem from the leaves (where they are made by photosynthesis) to the rest of the plant (e.g. roots, growing tips, storage organs).

What are monoclonal antibodies?

Monoclonal antibodies are identical antibodies produced from a single clone of cells. They are all specific to the same antigen (binding site), so they can be designed to target one particular molecule or cell type.

How are monoclonal antibodies produced in the laboratory?

1. A mouse is injected with the target antigen, stimulating it to produce lymphocytes (B cells) that make the specific antibody. 2. These lymphocytes are fused with tumour cells (myeloma cells) to make hybridoma cells. 3. Hybridoma cells can both divide rapidly (like tumour cells) and produce the antibody. 4. Individual hybridoma cells are cloned to produce large quantities of identical monoclonal antibodies.

What are hybridoma cells and why are they used?

Hybridoma cells are produced by fusing a lymphocyte (antibody-producing B cell) with a myeloma (tumour) cell. They combine the ability to produce a specific antibody with the ability to divide indefinitely, allowing large quantities of identical antibodies to be made.

How does a pregnancy test use monoclonal antibodies?

The test stick contains monoclonal antibodies specific to hCG (human chorionic gonadotropin), a hormone only present in the urine of pregnant women. If hCG is present, it binds to the antibodies and causes a colour change, producing a positive result line.

How can monoclonal antibodies be used to treat cancer?

Monoclonal antibodies can be attached to a radioactive substance, toxic drug, or chemical that blocks cell growth. They are designed to bind specifically to cancer cell antigens, delivering the treatment directly to tumour cells while leaving healthy cells unharmed. This is sometimes called a "magic bullet" approach.

How are monoclonal antibodies used to diagnose disease?

Monoclonal antibodies can be used in blood or tissue tests to detect the presence of specific antigens (e.g. cancer markers, pathogens). They can be tagged with a fluorescent dye so that the location of the target molecule can be identified in a tissue sample.

What is one advantage and one disadvantage of using monoclonal antibodies in medicine?

Advantage: they are highly specific, so they can target cancer cells or pathogens without damaging healthy tissue. Disadvantage: they can cause side effects such as fever, vomiting, or allergic reactions, and they are expensive and difficult to produce.

What is metabolism?

Metabolism is the sum of all the chemical reactions taking place inside the cells of an organism. It includes both reactions that build up molecules (anabolic reactions) and reactions that break them down (catabolic reactions).

Give four examples of metabolic reactions in the human body.

1. Aerobic and anaerobic respiration – breaking down glucose to release energy. 2. Synthesis of proteins from amino acids. 3. Synthesis of lipid molecules from glycerol and fatty acids. 4. Breaking down excess amino acids in the liver to form urea (for excretion).

How is the conversion of glucose into starch, glycogen, or cellulose an example of metabolism?

Plants convert glucose into starch for storage and cellulose for cell walls; animals convert glucose into glycogen for storage in the liver and muscles. These are all anabolic (building-up) metabolic reactions involving condensation reactions to form larger molecules.