AQA Biology GCSE - Topic 1: Cell Biology (Practice Flashcards)

A comprehensive set of practice questions and answers covering cell types, cell structure, microscopy, diffusion, osmosis, active transport, plant and animal adaptations, and stem cell biology from the notes.

What are the two main types of cells?

Prokaryotic and eukaryotic cells.

Which organisms have eukaryotic cells?

Animal and plant cells (and other eukaryotes) contain a nucleus and membrane-bound organelles.

What structures do bacterial (prokaryotic) cells have?

Cell wall, cell membrane, cytoplasm, a single circular DNA molecule and plasmids.

What are organelles?

Structures in a cell that have different functions.

Name three common organelles found in eukaryotic cells.

Cell membrane, cytoplasm, nucleus (also mitochondria and others as part of the organelle set).

What is the function of the nucleus?

Contains DNA that codes for proteins; enclosed in a nuclear membrane.

What is the function of chloroplasts?

Where photosynthesis takes place; contain chlorophyll that harvests light.

What is the function of mitochondria?

Where aerobic respiration occurs; provides energy for the cell.

What is the function of ribosomes?

Site of protein synthesis; found on the rough endoplasmic reticulum.

What is the function of the cell wall?

Provides strength and support; made from cellulose in plants.

What is the function of the permanent vacuole?

Contains cell sap and helps maintain cell rigidity.

What are plasmids?

Small rings of DNA found in bacterial cytoplasm.

How is prokaryotic DNA different from eukaryotic DNA?

Prokaryotes have no nucleus; DNA is circular and free in the cytoplasm, with plasmids.

What do prefixes centi, milli, micro, and nano represent (multipliers)?

Centi = 0.01; Milli = 0.001; Micro = 0.000001; Nano = 0.000000001.

What are the two main types of microscope?

Light microscope and electron microscope.

What are the two types of electron microscope and what do they produce?

SEM (scanning electron microscope) gives 3D images; TEM (transmission electron microscope) gives 2D images.

What is the maximum magnification and resolving power of a light microscope?

Magnification up to about x2000; resolving power ~ 200 nm.

How do you calculate the magnification of a light microscope?

Magnification = magnification of eyepiece lens × magnification of objective lens.

How do you calculate the size of an object from image size and magnification?

Size of object = size of image ÷ magnification.

What is standard form in science?

A way to express large or small numbers using powers of 10; the number multiplied by the power of 10 should be between 1 and 10.

How is population growth of bacteria commonly calculated?

Bacteria at beginning × 2^(number of divisions) = bacteria at end; divisions = time ÷ mean division time.

What is the zone of inhibition in antibiotic testing?

The clear area around a disc on an agar plate; a larger zone means more bacteria were killed.

What is mitosis?

The stage of the cell cycle where chromosomes are separated to form two identical daughter cells.

What are the stages of the cell cycle?

Interphase (growth, DNA replication), Mitosis (chromosome separation), Cytokinesis (cytoplasm division).

What is a gene?

A short section of DNA that codes for a protein and controls a characteristic.

How many chromosomes do human body cells have, and how many in gametes?

Body cells: 46 (23 pairs); gametes (sex cells): 23.

What are embryonic and adult stem cells?

Embryonic stem cells can differentiate into any type of cell; adult stem cells form many types but are more limited.

What are meristems in plants?

Plant stem cells found in root and shoot tips that can differentiate into any plant type; can be used to clone plants.

What is therapeutic cloning?

Producing an embryo with the patient's genes to obtain embryonic stem cells for transplantation.

What are the benefits and problems of stem cell research?

Benefits: replace damaged parts; problems: ethical concerns, incomplete understanding of differentiation, potential embryo destruction.

What is diffusion?

The spreading out of particles from an area of high concentration to an area of low concentration; passive (no energy).

What factors affect the rate of diffusion?

Concentration gradient (larger gradient → faster diffusion); temperature (higher → faster); surface area of membrane (larger → faster).

What is SA:V ratio and why is it important?

Surface area to volume ratio; large SA:V facilitates diffusion; multicellular organisms have smaller SA:V and need exchange surfaces.

What are alveoli and why are they important?

Tiny air sacs in the lungs with a large surface area for gas exchange (O2 in, CO2 out).

What are villi and why are they important?

Projections in the small intestine that increase surface area for absorption of digested food.

What are gills, lamellae, and why are they important in fish?

Gills have lamellae that increase surface area and enable gas exchange; water and blood flow in opposite directions to maintain a gradient.

What adaptations increase gas exchange in leaves and roots?

Leaves use a large surface area and stomata; root hairs increase surface area for water and mineral uptake.

What is the function of guard cells?

Control the size of stomata based on water availability to regulate gas exchange and water loss.

What is turgor pressure?

Pressure within plant cells from water in the vacuole that keeps leaves and stems rigid.

What is plasmolysis?

When plant cell membranes pull away from the cell wall in a hypertonic solution, leading to cell death.

What is osmosis?

The movement of water across a partially permeable membrane from high to low water potential (dilute to concentrated).

What happens to plant cells in hypotonic, isotonic, and hypertonic solutions?

Hypotonic: water moves in, plant cells become turgid; Isotonic: no net water movement; Hypertonic: water moves out, plant cells can plasmolyse.

What is active transport?

Movement of substances against the concentration gradient using energy from respiration; examples include uptake in root hairs and glucose absorption in the gut.

Why must sterile technique be used when culturing microorganisms?

To prevent contamination by unwanted microorganisms that could compete with or harm the cultures.

Why are Petri dishes incubated upside down?

To prevent condensation from dripping onto the agar surface and disrupting growth.