Topic 2 - Cells as the Basis of Life

What is cell theory?

A unifying theory stating that all living things are made of cells, and cells are the basic unit of structure and function in life.

What is the function of the cell membrane?

Separates the cytoplasm from its surroundings and controls the exchange of materials (nutrients and wastes) between the cell and its environment.

What is the fluid mosaic model?

A model describing the cell membrane as a flexible bilayer of phospholipids with proteins, cholesterol, and other molecules embedded throughout, where components can move within the layer.

What is a phospholipid bilayer?

Two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails facing inward, forming the basic structure of the cell membrane.

What are prokaryotic cells?

Cells with no membrane-bound nucleus or organelles, smaller in size, with circular DNA freely in the cytoplasm, and only existing as single cells (e.g. bacteria).

What are eukaryotic cells?

Cells with a membrane-bound nucleus and membrane-bound organelles, larger in size, with linear DNA organized into chromosomes within the nucleus.

How do prokaryotic and eukaryotic cells differ in size?

Prokaryotic cells are generally smaller (~0.1-5 micrometres) than eukaryotic cells (~10-100 micrometres).

What is the difference in internal organization between prokaryotic and eukaryotic cells?

Prokaryotic cells lack membrane-bound organelles; eukaryotic cells contain specialized membrane-bound organelles that compartmentalize functions.

What are the differences in chromosome structure between prokaryotic and eukaryotic cells?

Prokaryotic chromosomes are circular and located freely in the cytoplasm; eukaryotic chromosomes are linear and located within a membrane-bound nucleus.

What is the nucleus?

A membrane-bound organelle that houses the cell's genetic material (DNA) and controls gene expression and cell activities.

What is the nucleolus?

A structure inside the nucleus responsible for producing ribosomal RNA (rRNA) and assembling ribosomes.

What is the function of the mitochondrion?

An organelle with a folded inner membrane (cristae) that is the site of aerobic respiration, producing ATP for the cell.

What is the function of the chloroplast?

An organelle found in plant cells that contains chlorophyll and is the site of photosynthesis, converting light energy into chemical energy.

What is a vacuole/vesicle?

A membrane-bound sac used for storage, transport, or maintaining structure; for example, a large central vacuole in plant cells is used for water storage and turgor pressure.

What is the function of the Golgi body?

An organelle that modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

What is the rough endoplasmic reticulum?

A network of membranes studded with ribosomes; the site of protein synthesis and folding.

What is the smooth endoplasmic reticulum?

A network of membranes without ribosomes; involved in lipid synthesis and detoxification.

What is a ribosome?

A small structure (free in cytoplasm or attached to rough ER) responsible for protein synthesis (translation).

What is the function of a lysosome?

An organelle containing digestive enzymes used to break down waste materials, damaged organelles, and foreign particles.

What is the cytoskeleton?

A network of protein filaments that provides shape, structural support, and enables movement within the cell.

What are the distinguishing features of plant cells?

Cell wall (cellulose), large central vacuole, chloroplasts present, generally regular/fixed shape.

What are the distinguishing features of animal cells?

No cell wall, small/temporary vacuoles, no chloroplasts, irregular shape, may have centrioles.

What are the distinguishing features of fungal cells?

Cell wall (chitin, not cellulose), no chloroplasts, may contain vacuoles.

What is an autotroph?

An organism that produces its own food/organic molecules using energy from light (photosynthesis) or chemicals.

What is a heterotroph?

An organism that obtains energy by consuming other organisms or organic matter.

What is the equation for photosynthesis?

$6CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2$.

What is the equation for aerobic respiration?

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$.

What is fermentation (anaerobic) in plants/yeast?

Glucose is broken down without oxygen to produce ethanol, carbon dioxide, and a small amount of ATP.

What is fermentation (anaerobic) in animals?

Glucose is broken down without oxygen to produce lactic acid and a small amount of ATP.

How does aerobic respiration compare to anaerobic fermentation in terms of energy yield?

Aerobic respiration releases significantly more energy (ATP) per glucose molecule than fermentation, because fermentation only partially breaks down glucose.

What is the bond energy rule?

Energy is required to break chemical bonds; energy is released when new chemical bonds are formed.

How is ATP formed?

ATP (adenosine triphosphate) is formed from ADP (adenosine diphosphate) and an inorganic phosphate (Pi), storing energy in the new bond.

What happens during ATP breakdown?

ATP is converted back into ADP and Pi, releasing energy that powers metabolic reactions in the cell.

What is diffusion?

Passive movement of particles from an area of high concentration to an area of low concentration, down a concentration gradient, requiring no energy.

What is facilitated diffusion?

Passive movement of particles (e.g. large or charged molecules) across a membrane with the assistance of transport proteins, down a concentration gradient.

What is osmosis?

The diffusion of water molecules across a selectively permeable membrane, from an area of high water concentration to low water concentration.

What is active transport?

Movement of particles across a membrane against the concentration gradient (low to high concentration), requiring energy (ATP) and carrier proteins.

What is endocytosis?

Process by which a cell engulfs material from outside by folding the cell membrane around it, forming a vesicle inside the cell.

What is exocytosis?

Process by which a cell expels material by fusing a vesicle with the cell membrane and releasing the contents outside the cell.

What are channel proteins?

Transport proteins (e.g. aquaporins) that form pores allowing specific substances to passively move across the membrane.

What are aquaporins?

Channel proteins specifically allowing water molecules to move rapidly across the cell membrane.

What are carrier proteins?

Transport proteins that bind to specific molecules and change shape to move them across the membrane (used in facilitated diffusion and active transport).

What is the surface-area-to-volume ratio?

Smaller cells have a higher surface-area-to-volume ratio, allowing more efficient exchange of materials relative to their volume.

How does concentration gradient affect exchange?

A steeper concentration gradient increases the rate of diffusion/movement of substances across a membrane.

What factors affect exchange across membranes?

Surface-area-to-volume ratio of the cell, the concentration gradient, and the physical/chemical nature of the substance being exchanged.

How do internal membranes relate to metabolism?

The folded structure of mitochondrial cristae and chloroplast membranes increases surface area, enabling more efficient biochemical reactions (respiration and photosynthesis).

What is a metabolic pathway?

A series of regulated chemical reactions in a cell, where each step requires a specific enzyme, produces intermediate compounds, and loses some energy as heat.

What role do enzymes play in metabolic pathways?

Each step of a metabolic pathway requires a specific enzyme to catalyse the reaction.

What is a carcinogen?

A chemical or agent that causes mutations in genes that regulate the cell cycle, potentially leading to uncontrolled cell division (cancer).

What is binary fission?

Asexual reproduction process in prokaryotic cells where the cell duplicates its DNA and divides into two identical daughter cells.

What is mitosis?

The process of nuclear division in eukaryotic cells producing two genetically identical diploid daughter cells, used for growth and repair.

Why does DNA double before division?

DNA must replicate (double) before cell division so that each new daughter cell receives a complete and identical copy of the genetic material.

What are the products of binary fission and mitosis?

Binary fission (prokaryotes) and mitosis (eukaryotes) both produce two daughter cells genetically identical to the parent, with the same number and type of chromosomes.

What is a diploid cell?

A cell containing two complete sets of chromosomes (pairs of homologous chromosomes), one from each parent.

What is a haploid cell?

A cell containing only one set of chromosomes (one chromosome from each homologous pair).

What is meiosis?

The process of nuclear division in eukaryotic cells that produces four genetically unique haploid daughter cells (gametes), involving two divisions.

Why does meiosis produce haploid cells?

Meiosis involves two rounds of division following one round of DNA replication, halving the chromosome number so each gamete has a single set of chromosomes.

What is crossing over?

The exchange of genetic material between homologous chromosomes during meiosis, increasing genetic variation.

What is independent assortment?

The random distribution of homologous chromosomes into gametes during meiosis, increasing genetic variation.

What happens during fertilization?

Fertilization combines a haploid sperm and haploid egg to restore the diploid chromosome number in the resulting zygote.

What are the products of mitosis versus meiosis?

Mitosis produces 2 genetically identical diploid cells; meiosis produces 4 genetically unique haploid cells.

How do asexual and sexual reproduction differ in variation?

Asexual reproduction produces genetically identical offspring (low variation); sexual reproduction produces genetically varied offspring due to crossing over, independent assortment, and fertilization.

What is the cell cycle?

The sequence of growth, DNA replication, and division that a cell goes through, including checkpoints that regulate progression.

What are cell cycle checkpoints?

Internal control points in the cell cycle that check for errors (e.g. DNA damage) before allowing the cell to progress to the next stage.

How do hormones regulate cell division?

Hormones can signal cells to start or stop dividing, regulating the cell cycle externally.

What is cell culture?

A technique of growing cells outside their natural environment (in vitro) under controlled conditions, used in research, medicine, and production.

What is a hypothesis?

A testable statement predicting the relationship between variables in an investigation.

What is an independent variable?

The factor that is deliberately changed or manipulated in an experiment.

What is a dependent variable?

The factor that is measured and is expected to change as a result of the independent variable.

What are controlled variables?

Factors kept constant in an investigation so that only the independent variable affects the dependent variable, ensuring valid results.

What is an experimental control?

A baseline condition with no treatment, used for comparison to determine the true effect of the independent variable.

What is accuracy?

How close a measured value is to the true or accepted value.

What is precision?

How close repeated measurements are to each other.

What is reliability?

The consistency of results when an investigation is repeated.

What is validity?

Whether an investigation actually tests what it claims to test, with all variables controlled except the independent variable.

What is random error?

Unpredictable variation in measurements caused by uncontrollable factors, affecting precision.

What is systematic error?

A consistent, repeated error in the same direction, often caused by faulty equipment or method, affecting accuracy.

What is resolution in equipment?

The smallest increment of measurement that a piece of equipment can detect.

Why is sample size important?

Increasing sample size reduces the impact of random variation/error and increases the reliability of results.

What are some benefits of chemicals on cell metabolism?

Some chemicals humans use can have beneficial effects on cell metabolism, e.g. medicines and antibiotics that target specific metabolic pathways in pathogens.

What are some harmful effects of chemicals on cell metabolism?

Some chemicals can interfere with or disrupt cell metabolism, e.g. pesticides, pollutants, and certain drugs can inhibit enzymes or damage organelles.

What are the stages of the cell cycle?

Interphase (G1 - cell growth and normal function; S - DNA replication; G2 - further growth and preparation), followed by the Mitotic (M) phase (mitosis - nuclear division, then cytokinesis - cytoplasm division).

What is the G1 phase?

The first growth phase of interphase; cell grows, carries out normal functions, and is checked at the G1 checkpoint before DNA replication begins.

What is the S phase?

The synthesis phase of interphase; DNA is replicated so each chromosome is duplicated.

What is the G2 phase?

The second growth phase of interphase; cell continues to grow and prepares proteins/organelles needed for division, checked at the G2 checkpoint before mitosis.

What happens during the M phase (mitosis)?

The phase where the nucleus divides, followed by cytokinesis where the cytoplasm divides, producing two daughter cells.

What is the purpose of cell cycle checkpoints?

Checkpoints monitor cell size, DNA integrity, and chromosome attachment, halting the cycle if errors are detected to prevent faulty cell division.

What are cell culture techniques?

Methods used to grow cells outside the body in controlled conditions, including aseptic technique to prevent contamination.

What are the applications of cell culture?

Used in medical research, vaccine production, drug testing, tissue engineering, and producing cell lines for studying disease.

What are the limitations of cell culture?

Risk of contamination, cells may behave differently than in a living organism, high cost, and ethical considerations around sourcing cells.

How can systematic error be identified?

By calibrating equipment against a known standard, repeating the experiment with different equipment, or comparing results to an accepted value.

What are the limitations of conclusions?

Conclusions are limited by the sample size, the range of variables tested, the accuracy of equipment, and uncontrolled variables.

How should conclusions be formulated?

A conclusion should answer the hypothesis, based only on the data collected, reference specific trends, and acknowledge the limitations.