AQA A Level Biology Topic 2: Cells Practice Flashcards

Comprehensive vocabulary flashcards covering cell structure, microscopy, transport mechanisms, the cell cycle, and the immune system based on AQA A Level Biology Topic 2.

Eukaryotic Cells

Cells that contain a cytoplasm with membrane-bound organelles and $DNA$ enclosed in a nucleus.

Nucleus

Organelle that stores genetic information coding for polypeptides, serves as the site of $DNA$ replication and transcription ($mRNA$ production), and contains a nucleolus for making ribosomes / $rRNA$.

Ribosome

A non-membrane-bound organelle made of ribosomal $RNA$ and protein (two subunits) that serves as the site of protein synthesis (translation).

Rough Endoplasmic Reticulum (rER)

A system of membranes with ribosomes on the surface 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, such as cholesterol and steroid hormones.

Golgi Apparatus

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

Lysosomes

A type of Golgi vesicle that releases hydrolytic enzymes (e.g., lysozymes) to break down pathogens or worn-out cell components.

Miochondria

The site of aerobic respiration used to produce $ATP$ for energy release.

Chloroplasts

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

Cell Wall

A structure providing mechanical strength composed mainly of cellulose in plants and algae, or chitin in fungi, which prevents the cell from bursting due to osmosis.

Cell Vacuole

A plant organelle containing cell sap that maintains turgor pressure and stores 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.

Prokaryotic Cells

Unicellular organisms (bacteria and archaea) with cytoplasm lacking membrane-bound organelles and genetic material not enclosed in a nucleus.

Murein

A glycoprotein that composes the cell wall in all prokaryotic cells.

$70S$ Ribosomes

Smaller ribosomes found in prokaryotic cells, as well as in the mitochondria and chloroplasts of eukaryotic cells.

$80S$ Ribosomes

Larger ribosomes found in the cytoplasm of eukaryotic cells.

Acellular

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

Capsid

The protective protein coat that encloses the nucleic acid ($DNA$ or $RNA$) in a virus particle.

Magnification

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

Resolution

The minimum distance apart two objects can be to be distinguished as separate objects.

Transmission Electron Microscope (TEM)

A microscope that focuses electrons using electromagnets through a very thin specimen to generate a $2D$ cross-section with very high resolution.

Scanning Electron Microscope (SEM)

A microscope that bounces electrons off a specimen surface to generate a $3D$ image of the surface with high resolution.

Cell Fractionation

The process of breaking open cells to release contents, usually involving homogenisation and filtration followed by ultracentrifugation.

Ultracentrifugation

The process of separating organelles in order of density ($nuclei \rightarrow chloroplasts/mitochondria \rightarrow lysosomes \rightarrow ER \rightarrow ribosomes$) by spinning homogenate at increasing speeds.

Interphase

The stage of the cell cycle where $DNA$ replicates semi-conservatively ($S$ phase), organelle numbers increase, and protein synthesis occurs.

Mitosis

Division of the nucleus to produce two nuclei with identical copies of $DNA$.

Prophase

Stage of mitosis where chromosomes condense (visible as two sister chromatids joined by a centromere) and the nuclear envelope breaks down.

Metaphase

Stage of mitosis where spindle fibres attach to centromeres and chromosomes align along the equator.

Anaphase

Stage of mitosis where spindle fibres shorten and the centromere divides, pulling chromatids to opposite poles.

Telophase

Stage of mitosis where chromosomes uncoil, nuclear envelopes reform to create two nuclei, and spindle fibres break down.

Binary Fission

Replication in prokaryotic cells involving circular $DNA$ replication, plasmid replication, and division of the cytoplasm.

Mitotic Index (MI)

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

Fluid-Mosaic Model

Description of membrane structure where molecules like phospholipids, proteins, and glycoproteins move laterally in a bilayer.

Cholesterol

A component of cell membranes that bonds to phospholipid hydrophobic tails, restricting movement to decrease fluidity and increase rigidity.

Simple Diffusion

Passive movement of lipid-soluble or very small substances ($O_2$, steroid hormones) from high to low concentration across the phospholipid bilayer.

Facilitated Diffusion

Passive movement of water-soluble or charged substances down a concentration gradient through specific channel or carrier proteins.

Osmosis

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

Water Potential ($\nu$)

A measure of the likelihood of water molecules to move; pure distilled water has the maximum value of $0 kPA$.

Active Transport

The movement of substances against a concentration gradient requiring specific carrier proteins and the hydrolysis of $ATP$.

Co-transport

The simultaneous movement of two different substances via a carrier protein, such as the absorption of sodium ions ($Na^+$) and glucose in the ileum.

Antigen

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

Phagocytosis

Non-specific response where a phagocyte engulfs a pathogen into a phagosome, which then fuses with a lysosome to hydrolyse the pathogen using lysozymes.

Helper T Cells

T lymphocytes with complementary receptors that bind to antigens on antigen-presenting cells to stimulate cytotoxic T cells, B cells, and phagocytosis.

Humoral Response

The specific immune response involving B lymphocytes that divide by mitosis (clonal selection) to produce plasma cells and memory cells.

Antibody

A quaternary structure protein secreted by plasma cells that binds specifically to antigens at its variable region to form antigen-antibody complexes.

Agglutination

The clumping of pathogens caused by antibodies binding to two pathogens at once, which facilitates phagocytosis.

Active Immunity

Immunity requiring initial exposure to an antigen, resulting in the production of memory cells and long-term protection.

Passive Immunity

Short-term immunity provided by the introduction of antibodies from an external source (e.g., placenta or breast milk) without memory cell production.

Herd Immunity

Protection of unvaccinated individuals in a population when a large enough proportion is immune, reducing the spread of the pathogen.

Reverse Transcriptase

An enzyme released by $HIV$ that converts viral $RNA$ into $DNA$ within a host helper T cell.

Monoclonal Antibody

An antibody produced from genetically identical/cloned B lymphocytes, ensuring they all have the same tertiary structure.

ELISA Test

An enzyme-linked immunosorbent assay used to detect specific antigens or antibodies through a color change mediated by an enzyme-substrate reaction.