Biology Revision

CELLS (2)

8 Factors living things must fufill (MRSGREEN)

Movement
Respiration
Sensitivity
Growth
Reproduction
Equilibrium
Excretion
Nutrition

Cell theory

- all living things are made up of cells
- cells are the smallest and most basic unit of life
- all cells come from pre-exisiting cells

What do both prokaryotic cells and eukaryotic cells have

membrane
cytosol
ribosomes
DNA

What type of DNA do prokaryotes have

Single loop of DNA (circular)

What type of DNA do eukaryotes have

Multiple strand of linear DNA

What is/Role of plasma membrane

controls what can and cannot enter the cell

What is/Role of cytosol

contains salts, nutrients, and molecules (its fluid)

What is/Role of cytoplasm

cytosol and all organelles (not nucleus) make the cytoplasm

What is/Role of nucleus

double membrane, protect and confine DNA which codes for proteins

What is/Role of nucleolus

Site of ribosome production

What is/Role of ribosomes

rRNA and proteins, subunits makes proteins

What is/Role of rough endoplasmic reticulum

Synthesises and modifies proteins

What is/Role of smooth endoplasmic reticulum

Production of lipids

What is/Role of Golgi apparatus

Protein sorting, modifying and packaging

What is/Role of lysosome

breaks down cell waste and toxins

What is/Role of mitochondria

2 membrane, site of aerobic cellular respiration, producing ATP
- contains its own DNA and ribosomes

What is/Role of chloroplast

double membrane, site of photosynthesis, own DNA and ribosomes

What is/Role of Vacuole

water and solute storage, turgor pressure of cell

What is/Role of cell wall

sturdy border outside plasma membrane and provides strength and structure

What is/Role of vesicle

membrane bound sac that transports substances in/out of cell or stores them

What is/Role of cytoskeleton

Protein filament, maintaining shape and transporting vesicles around cell

Aerobic cellular respiration formula (worded and equation)

Glucose + oxygen -> carbon dioxide + water + energy
C6H12O6 + 6O2 -> 6CO2 + 6H2O + 36 ATP

Photosynthesis formula (worded and equation)

Carbon dioxide + water -> glucose + oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2

What happens during photosynthesis and where does it occur

Occurs in chloroplasts
Green pigment chlorophyll in chloroplast absorbs light to energise reactions
Glucose produced is used to build cell walls and carry out metabolic reaction
Excessive glucose stored in seeds as starch

Benefits of having small cells

Material exchange can occur efficiently due to high surface area to volume ratio
Distance to travel within cell is smaller so transport of molecules is faster

Is a larger of smaller SA:V ratio more efficient and why

larger - more exposed area

MEMBRANE (3)

What is the plasma membrane made of and what does it do

Made of (phospho)lipids and is selectively permeable to seperate intra and extracellular environment

What does the phospholipid bilayer contain

Proteins, carbohydrates and cholesterol

What is the Phospholipid head made of

Glycerol and phosphate group

What charge is the phospholipid head

negatively charged

Does the phospholipid head love or hate water (hydrophilic or phobic)

Hydrophilic - loves water - polar

What is the phospholipid tail made of

fatty acids

Does the phospholipid tail love or hate water (hydrophilic or phobic)

Hydrophobic - hates water - non-polar

What charge is the phospholipid tail

uncharged

Why are phospholipids stable

Because they are amphipathic - contain both hydrophobic and hydrophilic components

Functions of proteins in the membrane

Transport - channels and pumps control what enters/exits cell
Adhesion - Stick to other cells, extracellular matrix or cytoskeleton
Catalysis - speeds up chemical reaction with proteins (enzymes)
Communication - signals and regonise cells and molecules

Types of proteins and where are they in the membrane

Integral - permanent part of membrane
Transmembrane - Integral proteins which span entire bilayer
Peripheral - temporal attached to membrane

Structure of carbohydrates

In chains which extend outside of the cell
Rooted in membrane to lipids (glyco) or proteins (glyco)

Function of carbohydrates

Signalling and Communication with cell
Recognition of self or non-self molecules

Cholesterol structure

Lipid steroid embedded between fatty acid tails of phospholipid bilayer in animal cells

Role of cholesterol

Regulates membrane fluidity
- If hot keeps molecules bound together (phospholipids)
- If cold disrupts fatty acid tails, stopping phospholipids from being a solid boundary

What does the fluid mosaic model explain

Molecules in membrane are not static/ not held in one place
Different molecules embedded in membrane
Moves laterally (side to side)

What is diffusion

Movement of particles down a concentration gradient
- from area of high concentration to area of low concentration

What molecules can freely diffuse across the membrane

- non-polar
- uncharged
- hydrophobic
- small molecules (uncharged)

What leads to even particle distribution

Kinetic energy causes molecules to randomly move and bounce off each other, eventually leading to even particle distribution
- because of this higher temperatures = faster diffusion

What is a solute

thing being dissolved

What is a solvent

Thing being dissolved into

When is diffusion faster

When concentration gradient is steeper

What is facilitated diffusion and what does it allow

passive movement of molecules down the concentration gradient through a membrane bound protein (protein channel or carrier protein)
Allows larger/polar molecules to pass through membrane
STILL A PASSIVE PROCESS

What is a protein channel

Pores/holes in the membrane which let specific substances through

What is a carrier protein/what does it do

Binds to substance being transported and undergoes conformational change to push substance down concentration gradient through membrane
- returns to its original shape once the molecule is transported

What is Osmosis

Diffusion of water from area of low solute (high solvent) concentration to area of high solute (low solvent) concentration

Why can water diffuse through membrane if hydrophilic

Can diffuse because of their small size

What are protein channels for water called

Aquaporins

What is Hypertonic and the related movement of water

High solute concentration (water moves in)

What is Isotonic and the related movement of water

Equal solute concentration (no net movement of water)

What is Hypotonic and the related movement of water

Low solute concentration (water moves out)

What happens when animal cells fill with too much water (hypertonic)

Lysed - Too much water moves in and cell swells and bursts

What is active transport

Transporting substances across the membrane using energy

Does active transport go with or against the concentration gradient

Against

What does active transport require

Energy (ATP)
Membrane proteins - pumps and carriers

3 steps of active transport

- Binding - binds to specific protein pump
- Conformational change - energy released when bond is broken between 2nd and 3rd phosphate ions when ATP becomes ADP + P
- Release - pushed through protein and into other side of membrane

What is bulk transport

Movement of groups of molecules across plasma membrane using vesicles

What are the stages of Exocytosis

1. Vesicular transport - vesicle containing secretory products transported to plasma membrane
2. Fusion - membranes of vesicle and cell fuse
3. Release - Secretory products released from vesicle and leave cell

Why is Exocytosis possible

Because membrane is fluid and fuses with vesicle
When the vesicle fuses, it adds phospholipids and makes SA slightly bigger

What is Exocytosis

- contents of vesicle released from the cell

Why does the cell expand when exocytosis happens

Phospholipids are added to membrane

What is Endocytosis

- Transport into the cell

How is Endocytosis an effective defense mechanism

If invaded, a lysosome cans enter and digest invader

Endocytosis steps

1. Fold - membrane folds inwards and forms cavity that fills with extracellular fluid and target molecules
2. Trap - folds in on itself until 2 ends meet and fuse
3. Bud - Vesicle (endosome) pinches off from membrane

Why does the cell shrink when endocytosis happens

Phospholipids are removed from membrane

What is phagocytosis

Endocytosis of solid material or food particles

What is pinocytosis

Endocytosis of liquid or dissolved substances

CELL CYCLES (4)

Purpose of cell replication

- growth and development
- maintenance and repair
- reproduction

What does binary fission result in

2 genetically identical copies of a cell

Binary fission steps

1. DNA unclouded and replicated
2. Cell elongates and DNA duplicate move to opposite sides
3. Cytokinesis - pinches inwards and creates a septum
4. New wall and membrane formed down middle
5. seperate and 2 genetically identical cells are formed

Why aren't plasmids evenly distributed during binary fission

plasmids replicate Independently therefore aren't distributed evenly

What happens during Interphase

Cell synthesises the DNA, proteins and organelles required for growth/replication

What form is DNA in during Interphase

chromatin threads not chromosomes

What happens in the G1 phase

- Increase in cytosol volume
- Synthesising proteins for DNA replication
- Replicating its organelles
At the end, cell either proceeds to S or exits cell cycle and enters G0 phase

What happens during G0 phase

- cells which don't need to replicate rest here

What is a Quiescent cell

A cell which is dormant and can re-enter the cell cycle

Terminally Differentiated

A cell which is fully specialised and no longer replicates - remains in G0 indefinitely

What happens during the S phase

replicates DNA
- 1 chromosome becomes 2 genetically identical sister chromatids
- centromere holds them together

What happens during G2 phase

- increase of volume in cytosol
- synthesis proteins to prepare for mitosis

What are the 4 stages of Mitosis and in order

- Prophase
- Metaphase
- Anaphase
- Telophase

What happens at Prophase?

Condensation of chromatin so chromosomes become visible
Centrioles move to opposite poles
Spindle fibres begin to form
Nuclear membrane breaks down

What happens at Metaphase?

- Spindle fibres are fully formed and attach to each chromosomes centromere
- The fibres guide chromosomes to line up at equator of cell

What happens at Anaphase?

- spindle fibres contract and splits centromere
- sister chromatids pulled to opposite ends of cell

What happens at Telophase?

- spindle fibres disintegrate
- a cleavage furrow forms (animals)
- a cell plate forms (plants)

What happens at Cytokinesis?

Cytoplasm divides and and organelles evenly distribute before separating into daughter cells

What happens at the G1 checkpoint?

Checks if
- Cell has grown to correct size
- DNA has been damaged
- If there is sufficient nutrients for mitosis

What happens at the G2 checkpoint?

checks if
- DNA replicated properly in S phase
- Cell has enough resources for mitosis

What happens at the Metaphase checkpoint?

checks if
- Spindle fibres have formed and formed correctly
- Chromosomes are lined up in correct location

What are the 2 apoptotic pathways?

Mitochondrial (internal)
Death Receptor (external)

What detects internal damage in the mitochondrial pathway, and how does apoptosis then begin

Mitochondria - then releases cytochrome C to bind with proteins

What starts apoptosis in the death receptor pathway and what happens afterwards

Death signalling molecules are recognised by death receptor proteins on a cells surface (generally released by immune cells)

Molecules then bind to death receptor surface protein