test bio cells and biochemical

Cell

The basic structural and functional unit of life.

Main difference between prokaryotic and eukaryotic cells

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; eukaryotic cells have a membrane-bound nucleus and membrane-bound organelles.

Example of a prokaryotic organism

Bacteria.

Examples of eukaryotic organisms

Animals, plants, fungi and protists.

Prokaryotic

Literally "before nucleus"; the DNA is not enclosed in a membrane-bound nucleus.

Eukaryotic

Literally "true nucleus"; the DNA is enclosed within a membrane-bound nucleus.

Location of DNA in typical prokaryotic cell

In the nucleoid region of the cytoplasm; it is not enclosed by a nuclear membrane.

Plasmid

A small, usually circular piece of DNA separate from the main bacterial chromosome.

Function of plasmids

They can carry additional genes, such as genes for antibiotic resistance, and can be transferred between bacteria.

Structures common to both prokaryotic and eukaryotic cells

Plasma membrane, cytoplasm, ribosomes and DNA.

Function of the nucleus

It contains most of the cell's DNA and controls gene expression and cell activities.

Function of ribosomes

They are the sites of protein synthesis.

Function of mitochondria

They are the main site of aerobic cellular respiration and ATP production.

Function of chloroplasts

They are the site of photosynthesis in plants and algae.

Function of rough endoplasmic reticulum

It synthesises and transports proteins, with ribosomes attached to its surface.

Function of smooth endoplasmic reticulum

It is involved in lipid synthesis and other metabolic processes and lacks attached ribosomes.

Function of Golgi apparatus

It modifies, sorts and packages proteins and lipids into vesicles.

Function of lysosomes

They contain digestive enzymes that break down materials and cellular waste.

Function of vacuole in plant cells

It stores cell sap and helps maintain turgor pressure.

Function of cell wall in plants

It provides structural support and helps prevent the cell from bursting.

Cell wall in plants composition

Mainly made of cellulose.

Function of cytoplasm

It is the aqueous region where many metabolic reactions occur and where organelles are suspended.

Function of cytoskeleton

It maintains cell shape, positions organelles and helps with movement and intracellular transport.

Function of centrioles or centrosomes in animal cells

They help organise microtubules, particularly during cell division.

Plasma membrane

A selectively permeable boundary surrounding the cell that controls movement of substances into and out of the cell.

Fluid mosaic model

A model describing the plasma membrane as a dynamic phospholipid bilayer containing proteins and other components that can move within it.

Composition of a phospholipid

A hydrophilic phosphate head and two hydrophobic fatty acid tails.

Why phospholipids form a bilayer in water

Their hydrophilic heads interact with water while their hydrophobic tails avoid water and face inward.

Selectively permeable

The membrane allows some substances to cross more easily than others.

Simple diffusion

The net movement of particles from high concentration to low concentration directly through a membrane, without ATP.

Facilitated diffusion

The movement of substances down their concentration gradient through membrane proteins, without ATP.

Active transport

The movement of substances against their concentration gradient using energy, usually ATP, and transport proteins.

Osmosis

The net movement of water across a selectively permeable membrane from higher water potential to lower water potential.

Endocytosis

The uptake of material into a cell by the plasma membrane engulfing it and forming a vesicle.

Exocytosis

The release of material from a cell when a vesicle fuses with the plasma membrane.

Factors affecting the rate of diffusion

The concentration gradient, temperature, surface area, diffusion distance and properties of the substance or membrane.

Increasing surface area and diffusion rate

It provides more membrane through which particles can cross at the same time.

Why cells are small

A high surface-area-to-volume ratio allows efficient exchange of substances and heat with the environment.

ATP

Adenosine triphosphate, a readily usable energy-transfer molecule used to power cellular processes.

Photosynthesis

The process by which photosynthetic organisms use light energy to convert carbon dioxide and water into glucose, releasing oxygen.

Reactants of photosynthesis

Carbon dioxide and water, with light energy required.

Products of photosynthesis

Glucose and oxygen.

Location of photosynthesis

In chloroplasts of photosynthetic eukaryotic cells.

Role of chlorophyll

It absorbs light energy for photosynthesis.

Location of chlorophyll and other photosynthetic pigments

In the thylakoid membranes of chloroplasts.

Grana

Stacks of thylakoids in chloroplasts.

Stroma

The fluid-filled region of a chloroplast surrounding the thylakoids, where the Calvin cycle occurs.

Two broad stages of photosynthesis

The light-dependent reactions and the Calvin cycle.

Location of light-dependent reactions

In the thylakoid membranes of chloroplasts.

Products of light-dependent reactions

ATP and NADPH, while water is split and oxygen is released.

Photolysis

The light-driven splitting of water, producing electrons, hydrogen ions and oxygen.

Location of Calvin cycle

In the stroma of the chloroplast.

Calvin cycle uses

Carbon dioxide, ATP and NADPH to produce carbohydrate molecules.

Main limiting factors of photosynthesis

Light intensity, carbon dioxide concentration and temperature.

Increasing light intensity when light is limiting

It increases the rate of photosynthesis until another factor becomes limiting.

Increasing CO2 concentration when CO2 is limiting

It increases the rate until another factor becomes limiting.

High temperatures and photosynthesis

Photosynthetic enzymes can lose their functional shape and other cellular processes can be disrupted.

Cellular respiration

A series of enzyme-controlled reactions that release energy from organic molecules and transfer much of it into ATP.

Aerobic respiration

Cellular respiration that uses oxygen as the final electron acceptor and produces much more ATP than anaerobic pathways.

Reactants of aerobic respiration

Glucose and oxygen.

Products of aerobic respiration

Carbon dioxide, water and energy transferred to ATP and released as heat.

Location of glycolysis

In the cytosol or cytoplasm.

Glycolysis process

One glucose molecule is split into two pyruvate molecules, producing a small net amount of ATP and reduced electron carriers.

Glycolysis and oxygen

Glycolysis itself does not directly require oxygen.

Location of Krebs cycle in eukaryotic cells

In the mitochondrial matrix.

Krebs cycle process

Acetyl-CoA is oxidised, producing carbon dioxide, ATP and reduced electron carriers such as NADH and FADH2.

Electron transport chain location in aerobic respiration

In the inner mitochondrial membrane.

Oxygen role in aerobic respiration

It acts as the final electron acceptor in the electron transport chain and combines with electrons and hydrogen ions to form water.

Chemiosmosis in cellular respiration

The movement of H+ down an electrochemical gradient through ATP synthase, driving ATP production.

Oxidative phosphorylation

ATP production linked to the electron transport chain and chemiosmosis.

Inner mitochondrial membrane folds

Folds increase membrane surface area for electron transport proteins and ATP synthase.

NADH and FADH2

Reduced electron carriers that transport high-energy electrons to the electron transport chain.

Glucose during aerobic respiration

It is progressively oxidised, ultimately producing carbon dioxide while electrons are transferred to carriers and ATP is generated.

Anaerobic respiration or fermentation

Energy-releasing pathways that operate without oxygen, allowing glycolysis to continue by regenerating NAD+.

Pyruvate in human muscle cells without sufficient oxygen

It is converted to lactate, regenerating NAD+ so glycolysis can continue.

Alcoholic fermentation in yeast

Pyruvate is converted to ethanol and carbon dioxide, regenerating NAD+.

Fermentation ATP production

It produces much less ATP than aerobic respiration; only glycolysis directly produces ATP.

Link between photosynthesis and cellular respiration

Photosynthesis stores light energy in glucose, while cellular respiration releases usable energy from glucose into ATP; their overall reactants and products are closely connected.

Chloroplasts vs mitochondria

Chloroplasts capture light energy to make organic molecules; mitochondria extract usable energy from organic molecules through respiration.

Chloroplasts, enzymes, and respiration

Chloroplasts provide specialised membranes and compartments, while enzymes catalyse the chemical reactions.

Respiration as an enzyme-controlled process

Each stage consists of specific reactions catalysed by enzymes, allowing the pathway to be regulated.

Relationship between ATP and ADP

ATP can release energy when converted to ADP and phosphate; energy can be used to regenerate ATP from ADP and phosphate.

Cells' need for ATP over glucose

ATP provides a readily transferable and controllable form of energy for cellular work.

Comparison of prokaryotic and eukaryotic ribosomes

Both make proteins, but bacterial or prokaryotic ribosomes are generally smaller (70S) than cytoplasmic eukaryotic ribosomes (80S).

Do prokaryotes have mitochondria or chloroplasts?

No. They lack membrane-bound organelles; their respiration and photosynthetic processes, when present, occur using the plasma membrane or specialised internal membranes.

Nucleoid

The region of a prokaryotic cell containing its main chromosome; it is not surrounded by a membrane.

Difference between cell wall and plasma membrane

The cell wall provides external structural support, while the plasma membrane is a selectively permeable boundary controlling transport.

Why membrane proteins have different functions

Their structures allow them to act as channels, carriers, pumps, receptors, enzymes or cell-recognition molecules.

Concentration gradient

A difference in concentration of a substance between two regions.

Direction of net passive diffusion

Down the concentration gradient, from higher concentration to lower concentration.

Difference between passive and active transport

Passive transport does not require cellular energy and moves substances down their gradient; active transport requires energy and can move substances against their gradient.