Cells

What is a eukaryotic cell?

A cell containing a nucleus and membrane-bound organelles.

What is a prokaryotic cell?

A cell without a nucleus or membrane-bound organelles.

What is the function of the nucleus?

Contains genetic material and controls cell activities.

What is the function of the nucleolus?

Produces ribosomal components.

What is the function of the nuclear envelope?

Separates the nucleus from the cytoplasm and contains pores for exchange of substances.

What is the function of mitochondria?

Site of aerobic respiration and ATP production.

What is the function of chloroplasts?

Site of photosynthesis.

What is the function of rough endoplasmic reticulum?

Synthesises and transports proteins using attached ribosomes.

What is the function of smooth endoplasmic reticulum?

Synthesises and processes lipids.

What is the function of the Golgi apparatus?

Modifies and packages proteins into vesicles.

What is the function of lysosomes?

Contain hydrolytic enzymes that digest unwanted materials.

What is the function of ribosomes?

Site of protein synthesis.

What is the function of the cell wall in plants?

Provides structural support and prevents bursting due to water uptake.

What is the plant cell wall made of?

Cellulose.

What is the function of the permanent vacuole?

Contains cell sap and maintains turgor pressure.

What is the function of the cell-surface membrane?

Controls movement of substances into and out of cells.

What is the function of the cytoskeleton?

Provides mechanical strength and enables movement of organelles and cell contents.

What is the function of centrioles?

Organise spindle fibres during cell division.

What is the function of the flagellum?

Enables cell movement.

What is the function of cilia?

Move substances across cell surfaces.

What is the function of microvilli?

Increase surface area for absorption.

What are the main structures of a prokaryotic cell?

Cell wall, cell-surface membrane, cytoplasm, ribosomes, circular DNA and sometimes plasmids, capsule or flagella.

What is the composition of bacterial cell walls?

Murein.

What are plasmids?

Small circular DNA molecules found in some bacteria.

What is the function of a bacterial capsule?

Provides protection against environmental conditions and host defences.

How do prokaryotic ribosomes differ from eukaryotic ribosomes?

Prokaryotes have smaller 70S ribosomes; eukaryotic cytoplasmic ribosomes are 80S.

How is DNA arranged in prokaryotes?

As a circular DNA molecule free in the cytoplasm.

What are viruses?

Acellular particles containing nucleic acid enclosed in a protein coat.

What structures may viruses contain?

Genetic material, capsid, attachment proteins and sometimes a lipid envelope.

Why can viruses only reproduce inside living cells?

They lack the cellular machinery needed for independent replication.

What is the difference between magnification and resolution?

Magnification is enlargement; resolution is the ability to distinguish two close points.

What is the magnification formula?

Magnification = image size ÷ actual size.

How do you calculate actual size?

Actual size = image size ÷ magnification.

How many nanometres are in one micrometre?

1000 nm.

How many micrometres are in one millimetre?

1000 µm.

What is the advantage of electron microscopes over light microscopes?

Higher resolution allows smaller structures to be distinguished.

What is the function of a transmission electron microscope (TEM)?

Produces detailed two-dimensional images of internal cell structures.

What is the function of a scanning electron microscope (SEM)?

Produces three-dimensional images showing surface detail.

Why do electron microscopes have higher resolution?

Electrons have a shorter wavelength than visible light.

What is cell fractionation?

The process of separating cellular components for examination.

What is homogenisation?

Breaking open cells to release organelles.

Why is the homogenisation solution ice-cold?

To reduce enzyme activity and prevent organelle damage.

Why is the homogenisation solution isotonic?

To prevent organelles shrinking or bursting due to osmosis.

Why is the homogenisation solution buffered?

To maintain a constant pH and prevent protein denaturation.

What is ultracentrifugation?

Separating cell components by spinning at progressively higher speeds.

What happens during differential centrifugation?

Larger organelles sediment first; smaller organelles require higher speeds.

What is the pellet?

The solid material collected at the bottom of a centrifuge tube.

What is the supernatant?

The liquid remaining above the pellet.

What is the cell cycle?

The sequence of events involving cell growth, DNA replication and cell division.

What happens during interphase?

Cell growth, DNA replication and organelle replication.

What happens during prophase?

Chromosomes condense, the nuclear envelope breaks down and spindle fibres form.

What happens during metaphase?

Chromosomes align at the cell equator and attach to spindle fibres.

What happens during anaphase?

Sister chromatids separate and move to opposite poles.

What happens during telophase?

Nuclear envelopes reform and chromosomes begin to uncoil.

What is cytokinesis?

Division of the cytoplasm to form two daughter cells.

What is mitosis?

Nuclear division producing two genetically identical daughter nuclei.

Why is mitosis important?

Growth, tissue repair and asexual reproduction.

What is a chromosome?

A DNA molecule associated with proteins.

What are sister chromatids?

Identical copies of a replicated chromosome joined at a centromere.

What is the mitotic index?

Number of cells in mitosis ÷ total number of cells.

What is binary fission?

Asexual reproduction in prokaryotes involving DNA replication and division into two cells.

How do viruses replicate?

They attach to host cells, enter or inject genetic material, use host machinery to produce components and assemble new viruses.

What is the fluid mosaic model?

A model describing membranes as a phospholipid bilayer containing proteins that can move laterally.

Why do phospholipids form a bilayer?

Hydrophilic heads face water while hydrophobic tails face inward away from water.

What is the role of cholesterol in cell membranes?

Regulates membrane fluidity and reduces permeability to some substances.

What is the role of channel proteins?

Allow specific ions or polar molecules to cross membranes by facilitated diffusion.

What is the role of carrier proteins?

Bind specific substances and change shape to transport them across membranes.

What is the role of glycoproteins?

Act as receptors and cell-recognition molecules.

What is the role of glycolipids?

Help with cell recognition and membrane stability.

What is diffusion?

Net movement of particles from higher to lower concentration down a concentration gradient.

What factors increase diffusion rate?

Larger surface area, steeper concentration gradient and shorter diffusion distance.

What is facilitated diffusion?

Passive movement down a concentration gradient through channel or carrier proteins.

Does facilitated diffusion require ATP?

No.

What is osmosis?

Net movement of water molecules across a partially permeable membrane from higher to lower water potential.

What is water potential?

A measure of the tendency of water molecules to move from one region to another.

What is the water potential of pure water?

Zero kPa.

In which direction does water move by osmosis?

From higher water potential to lower water potential.

What happens to an animal cell in a hypotonic solution?

Water enters and the cell may burst.

What happens to an animal cell in a hypertonic solution?

Water leaves and the cell shrinks.

What happens to a plant cell in a hypotonic solution?

Water enters and the cell becomes turgid.

What happens to a plant cell in a hypertonic solution?

Water leaves and the cell becomes plasmolysed.

What is active transport?

Movement of substances against a concentration gradient using ATP and carrier proteins.

What is co-transport?

Transport of two substances together using a concentration gradient established by active transport.

How are glucose and sodium ions co-transported in the ileum?

Sodium ions are actively transported out of epithelial cells; sodium ions then move in from the lumen through co-transport proteins carrying glucose.

What is an antigen?

A molecule recognised as foreign by the immune system that can trigger an immune response.

What is cell recognition?

Identification of cells using specific molecules on their surfaces.

What is the role of cell-surface antigens?

Allow the immune system to distinguish between different cells.

What is phagocytosis?

Engulfment and digestion of pathogens by phagocytes.

What happens during phagocytosis?

A phagocyte engulfs a pathogen into a vesicle; lysosomes fuse with it and enzymes digest the pathogen.

What is the role of T helper cells?

Stimulate B cells and other immune cells using cytokines.

What is the role of cytotoxic T cells?

Destroy infected or abnormal body cells.

What is the role of B cells?

Differentiate into plasma cells and memory cells following activation.

What are plasma cells?

Activated B cells that secrete antibodies.

What are memory cells?

Long-lived lymphocytes that enable a faster secondary immune response.

What is an antibody?

A protein produced by plasma cells that binds specifically to an antigen.

What determines antibody specificity?

The shape of the variable region and its complementary binding site.

What is the primary immune response?

The initial response to an antigen, producing antibodies and memory cells.

What is the secondary immune response?

A faster and larger antibody response following subsequent exposure to the same antigen.

What is active immunity?

Immunity produced when an individual's immune system responds to an antigen.

What is passive immunity?

Immunity obtained by receiving antibodies produced by another organism.