AQA A Level Biology Topic 2: Cells Practice Flashcards

Comprehensive vocabulary flashcards covering AQA A Level Biology Topic 2, including cell structure, transport, division, and the immune system.

Distinguishing features of eukaryotic cells

Cytoplasm containing membrane-bound organelles and DNA enclosed in a nucleus.

Cell-surface membrane function

Selectively permeable to control passage of substances and contains molecules/receptors/antigens for cell recognition and signalling.

Nucleus function

Holds/stores genetic information coding for polypeptides, site of DNA replication and transcription (producing mRNA), and the nucleolus makes ribosomes/rRNA.

Ribosome

A non-membrane-bound organelle made of ribosomal RNA and protein (two subunits) which is the site of protein synthesis (translation).

Rough endoplasmic reticulum (rER)

Organelle with surface ribosomes that synthesise proteins, which are then processed, folded, and packaged into vesicles for transport.

Smooth endoplasmic reticulum (sER)

Organelle that synthesises, processes, transports, and packages lipids and carbohydrates.

Golgi apparatus function

Modifies proteins (e.g., adding carbohydrates to produce glycoproteins) and lipids, packages them into Golgi vesicles, and produces lysosomes.

Golgi vesicles

Structures that transport proteins or lipids to required destinations, such as the cell-surface membrane.

Lysosomes

Golgi vesicles that release hydrolytic enzymes (e.g., lysozymes) to break down pathogens or worn-out cell components.

Mitochondria function

Site of aerobic respiration to produce ATP for energy release (e.g., for protein synthesis or active transport).

Chloroplasts

Organelles in plants and algae containing pigments like chlorophyll to absorb light energy for photosynthesis to produce organic substances.

Cell wall composition

Composed mainly of cellulose in plants and algae, and chitin (a nitrogen-containing polysaccharide) in fungi.

Cell vacuole function

Maintains turgor pressure to stop plant wilting and contains cell sap to store sugars, amino acids, pigments, and waste chemicals.

Tissue

A group of specialised cells with a similar structure working together to perform a specific function.

Organ

Aggregations of tissues performing specific functions.

Distinguishing features of prokaryotic cells

Cytoplasm lacking membrane-bound organelles and genetic material not enclosed in a nucleus.

Murein

A glycoprotein that makes up the cell wall in all prokaryotic cells.

Acellular

A term describing viruses meaning they are not made of cells and have no cell membrane, cytoplasm, or organelles.

Viral capsid

A protective protein coat that encloses the nucleic acid (DNA or RNA) of a virus particle.

Magnification

The number of times greater an image is than the size of the real object, calculated as $\text{size of image} / \text{size of real object}$.

Resolution

The minimum distance apart two objects can be to be distinguished as separate objects (level of detail).

Optical microscope characteristics

Uses light and glass lenses, has low resolution due to the long wavelength of light, low magnification ($\times 1500$), and can view living organisms in colour.

Transmission electron microscope (TEM)

Uses electromagnets to pass electrons through a very thin specimen; provides 2D cross-sections with very high resolution and high magnification ($\times 1,000,000$) but requires a vacuum.

Scanning electron microscope (SEM)

Uses electromagnets to bounce electrons off a specimen surface; generates a 3D image with high resolution and high magnification ($\times 1,000,000$) but requires a vacuum.

Interphase

Stage of the cell cycle where DNA replicates semi-conservatively (S phase), organelle numbers increase, and protein synthesis occurs (G1/G2).

Mitosis

Division of the nucleus to produce two nuclei with identical copies of DNA produced by the parent cell.

Prophase

Phase where chromosomes condense (becoming shorter, thicker, and visible as sister chromatids), nuclear envelope breaks down, and centrioles form a spindle network.

Metaphase

Phase where chromosomes align along the equator and spindle fibres attach to their centromeres.

Anaphase

Phase where spindle fibres shorten, centromeres divide, and chromatids are pulled to opposite poles.

Telophase

Phase where chromosomes uncoil (becoming longer and thinner), nuclear envelopes reform to create two nuclei, and spindle fibres break down.

Binary fission

The process by which prokaryotic cells replicate, involving replication of circular DNA and plasmids followed by division of the cytoplasm.

Mitotic index (MI)

The proportion of cells undergoing mitosis in a sample, calculated as $\text{number of cells undergoing mitosis} / \text{total number of cells in sample}$.

Fluid-mosaic model

Describes membrane structure where molecules are free to move laterally in a phospholipid bilayer containing proteins, glycoproteins, and glycolipids.

Cholesterol (in membranes)

Molecules that bond to phospholipid fatty acid tails to restrict movement, decreasing fluidity and increasing rigidity.

Simple diffusion

The passive movement of lipid-soluble (non-polar) or very small substances down a concentration gradient across the phospholipid bilayer.

Facilitated diffusion

The passive movement of water-soluble, polar, or charged substances across a membrane through specific channel or carrier proteins.

Osmosis

The passive diffusion of water from an area of high water potential to low water potential through a partially permeable membrane.

Water potential ($\psi$)

A measure of how likely water molecules are to move out of a solution; pure water has the maximum value of $0,kPa$.

Active transport

Movement of substances from an area of lower to higher concentration (against a gradient) requiring the hydrolysis of ATP and specific carrier proteins.

Co-transport

The simultaneous movement of two different substances via a co-transporter protein, often coupling the movement of one down its gradient with another against its gradient.

Antigen

A foreign molecule (protein, glycoprotein, or glycolipid) that stimulates an immune response leading to the production of antibodies.

Phagocytosis

Process where a phagocyte engulfs a pathogen into a phagosome, which then fuses with a lysosome whose lysozymes hydrolyse the pathogen.

T lymphocytes (Cellular response)

Cells that recognise antigens on antigen-presenting cells; helper T cells stimulate cytotoxic T cells, B cells, and phagocytes.

B lymphocytes (Humoral response)

Cells that undergo clonal selection when complementary receptors bind to antigens, dividing by mitosis to form plasma cells (secreting antibodies) or memory cells.

Antibody

A quaternary structure protein secreted by B lymphocytes that binds specifically to antigens to form antigen-antibody complexes.

Agglutination

The clumping of pathogens caused by antibodies binding to two pathogens at once, which attracts phagocytes.

Vaccine

The introduction of antigens (e.g., from attenuated pathogens) to stimulate the formation of memory cells.

Herd immunity

Protection for a population where a large proportion is vaccinated, reducing the spread of a pathogen and protecting unvaccinated individuals.

Active vs. Passive immunity

Active immunity involves initial antigen exposure and memory cell production (long-term); passive immunity involves introduced antibodies without memory cells (short-term).

Reverse transcriptase

An enzyme in HIV that converts viral RNA into DNA once it has entered a host cell.

Monoclonal antibody

An antibody produced from genetically identical (cloned) B lymphocytes, ensuring all have the same tertiary structure and binding site.

ELISA test

Enzyme-linked immunosorbent assay; a test using antibodies with attached enzymes to detect the presence of specific antigens or antibodies through a color change.