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Prokaryotic cells
Bacteria cells (much smaller than Euk)
-Cell wall
-Cell membrane
-Cytoplasm
-Singular strands of DNA and plasmids (found in cytoplasm)
Eukaryotic cells
Animal and Plant Cells
-Cell Membrane
-Cytoplasm
-Nucleus (containing DNA)
Organelles
structures in a cell that have different functions
Units of measurement
Multiplying Factor | Name (symbol) | Scientific Notation |
|---|---|---|
0.01 | centi (c) | 10-2 |
0.001 | milli (m) | 10-3 |
0.000 001 | micro (µ) | 10-6 |
0.000 000 001 | nano (n) | 10-9 |
Nucleus - plant, animal
-Contains DNA coding for a particular protein needed to build new cells.
- Enclosed in a nuclear membrane.
Cytoplasm - plant, animal, bacteria
-Liquid substance in which chemical reactions occur.
-Contains enzymes (biological catalysts, i.e. proteins that speed up
the rate of reaction).
-Organelles are found in it
Cell Membrane - plant, animal, bacteria
Controls what enters and leaves the cell
Mitochondria - plant, animal
Where aerobic respiration reactions occur, providing energy for the cell
Ribosomes - plant, animal
- Where protein synthesis occurs.
- Found on a structure called the rough endoplasmic reticulum
Chloroplasts - plant
-Where photosynthesis takes place, providing food for the plant
-Contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis.
Permanent Vacuole - plant
-Contains cell sap
-Found within the cytoplasm
-Improves cell’s rigidity
Cell wall - plant, algal
-Made from cellulose
-Provides strength to the cell
Cell wall - bacteria
-Made of a different compound
(peptidogylcan)
Singular circular strand of DNA - bacteria
-As they have no nucleus, this floats in the cytoplasm
Plasmids - bacteria
small rings of DNA
What is cell specialisation?
Where cells gain new sub-cellular structures in order to be suited to their role.
Cells can either differentiate once early on or have the ability to differentiate their whole life (these are called stem cells)
How are sperm cells specialised to to carry the male’s DNA to the egg cell (ovum) for successful reproduction
Animals
-Streamlined head and long tail to aid swimming
-Many mitochondria (where respiration happens) which supply the energy to allow the cell to move
-The acrosome (top of the head) has digestive enzymes which break down the outer layers of membrane of the egg cell
How are nerve cells specialised to transmit electrical signals quickly from one place in the body to another
Animals
-The axon is long, enabling the impulses to be carried along long distances
-Having lots of extensions from the cell body (called dendrites) means branched connections can form with other nerve cells
-The nerve endings have many mitochondria which supply the energy to make special transmitter chemicals called neurotransmitters. These allow the impulse to be passed from one cell to another.
How are muscle cells specialised to contract quickly to move bones (striated muscle) or simply to squeeze (smooth muscle, e.g found in blood vessels so blood pressure can be varied), therefore causing movement
animals
-Special proteins (myosin and actin) slide over each other, causing the muscle to contract
-Lots of mitochondria to provide energy from respiration for contraction
-They can store a chemical called glycogen that is used in respiration by mitochondria
How are root hair cells specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots
Plants
-Have a large surface area due to root hairs, meaning more water can move in
-The large permanent vacuole affects the speed of movement of water from the soil to the cell
-Mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell
How are Xylem cells specialised to transport water and mineral ions up the plant from the roots to the shoots
Plants
-Upon formation, a chemical called lignin is deposited which causes the cells to die. They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through
-Lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water
How are Phloem cells: specialised to carry the products of photosynthesis (food) to all parts of the plants
Plants
-Cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell
-Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells.
What is Cell Differentiation in stem cells?
-Stem cells must undergo cell differentiation to become specialised cells
-This means some of their genes are switched on/off to produce different proteins
Cell differentiation in animals
-Happens early in most animal cells (then they lose ability)
-Most specialised cells reproduce through mitosis
-Others (red blood cells) can’t divide so are replaced by adult stem cells
-In mature animals, cell division mostly only happens to repair or replace damaged cells, as they undergo little growth. C
Cell differentiation in plants
-Most plant cells keep ability for life
-Only differentiate when reach final position
Light Microscope
-Robert Hooke, 1665
-2 Lenses: objective and eyepiece
-Illuminated from underneath
-Max. magnification of x2000
-Resolving power of 200nm
-Used to view tissues, cells, large sub-cellular structures
How do the lenses of a Light Microscope work?
The objective lense produces a magnified image, which is then magnified and directed into the eye by the eyepiece lense
Electron microscope
-Used to view deep inside inside sub-cellular structures, such as mitochondria, ribosomes, chloroplasts and plasmids.
-Electrons are used to form an image because they are opposed to light (much smaller wavelength than light waves)
-Magnification of up to 2,000,000, resolving power of 10nm
Types of electron microscope
-Scanning electron microscope: creates 3D images (lower magnification)
-Transmission electron microscope: creates 2D mages detailing organelles
Magnification of a light microscope
magification of eyepiece lens x magnification of objective lens
Size of an object
size of image / magnification
How many pairs of chromosomes in each cell?
23 pairs (each with 1 mother and 1 father)
Sex cells are the exception (half)
The cell cycle stage 1
Interphase: cell grows, organelles grow and increase in number, synthesis of proteins occurs, DNA is replicated (Forms X shape) ,energy stores increased
The cell cycle stage 2
Mitosis: Chromosomes line up at the equator of the cell
Cell fibres pull each chromosome of the ‘X’ to either side of the cell
The cell cycle stage 3
Cytokinesis: Two identical daughter cells form when cytoplasm and cell membranes divide
Why is cell division by mitosis important?
-Growth and development
-Replacing damaged cells
-Asexual reproduction
Types of stem cells
-Embryonic (egg and sperm fuse)
-Adult (form many types of cells)
-Meristems (Root and shoot tips)
Therapeutic Cloning
-Embryo produced with the same genes as patient
-Embryo could be harvested to obtain embryotic stem cells, then grown into cells patient needed (new tissues / organs)
-Advantage: would not be rejected
Benefits of research w/ Stem cells
-Can be used to replace damaged/ diseased body parts
-Unwanted embryos could be used
-Research into process of differentiation
Problems of research w/ Stem cells
-We don’t understand it completely (hard to control)
-Destruction of embryo
-Religious/ Ethical objections
-Stem cells contaminated → individual contaminated
-Money / time consumed
Diffusion
the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of
higher concentration to an area of lower concentration
What do molecules have to be in diffusion?
Small: to be able to move across
Examples of diffusion in the body
Oxygen moves through alveoli into red blood cells, carried to cells across the body → respiration.
CO2 moves from red blood cells → lungs to be exhaled
^ called GAS EXCHANGE
Factors affecting rate of diffusion
-Concentration gradient: greater gradient = faster rate (more particles randomly moving down gradient than against it)
-Temperature greater temp = greater movement (more collisions)
-Surface area of membrane: greater SA = more space for particles, faster diffusion
Why can Single-celled organisms use diffusion to transport molecules into their body from the air?
Relatively large SA to Volume ratio
Why can’t multicellular organisms rely on diffusion alone?
-Small SA to Volume ratio
-Instead they have many adaptations (allow molecules to be transported in and out of cells)
Examples of adaptations to assist diffusion (large SA)
-Lungs: O2 →blood, CO2 →Lungs. Takes place across alveoli, covered in capillaries (supply blood)
-Small intestine: digested food absorbed over membrane of villi
-Gills: gas exchange takes place in fish, gill has gill filaments
Osmosis
the movement of water from a less concentrated solution to a more concentrated one through a partially permeable membrane.
3 features of a good scientific drawing
Scale, Accuracy, Labels
How can scientists study microorganisms?
Microorganisms are very small - scientists need to grow them in a lab using nutrients (culture them)
What does the culture medium contain?
carbohydrates for energy, minerals, proteins and vitamins
Ways to grow microorganisms in the lab?
Nutrient broth solution
Agar gel plate
Nutrient broth solution
making a suspension of bacteria to be grown, mixing with sterile nutrient broth (culture medium), stoppering flask with cotton wool (prevent air from contaminating), shaking regularly to provide oxygen for growing bacteria
Agar gel plate
agar acts as culture medium, bacteria grown on it form colonies on the surface
to make the plate: hot jelly poured into petri dish, left to cool and set (all sterilised)
wire loops (inoculating loops) dipped in a solution of microorganism and spread over agar evenly
lid taped on, plate incubated for a few days (microorganisms can grow)
Why is the petri dish and culture media sterilised before use? (usually done by autoclave)
likely to be contaminated (other microorganisms can compete with desired bacteria)
Why is inoculating loop sterilised?
Kills unwanted organisms
Lid of petri dish is sealed because..
stops airborne microorganisms from contaminating culture
should not be sealed all the way (harmful anaerobic bacteria)
Petri dish is stored upside down because…
will prevent condensation from the lid landing on the agar surface & disrupting growth
Why should the culture be incubated at 25 degrees?
if temp was higher (nearer 37 - human body temp), more likely bacteria that could be harmful to humans would be able to grow (optimum temp)
Why does water move from dilute to concentrated?
area of high water potential → low water potential (down concentration gradient)
osmosis is PASSIVE (doesn’t use energy)
Why will water move into our cells?
Cytoplasm contains salts and sugars so when cell is placed in dilute solution, water moves inH
Hypertonic solution
any external solution that has a high solute concentration and low water concentration compared to body fluids
Isotonic soluion
any external solution that has the same solute concentration and water concentration compared to body fluids
Osmosis in animals
-External solution dilute = move into animal cells and they will burst
-External solution concentrated = water leave cell causing it to become shrivelled
Osmosis in plants
-External solution more dilute = water moves into cell and vacuole (swell, turgor)
-External solution less dilute = water moves out of cell, becomes soft. eventually cell membrane moves away from cell wall and it will die
Active transport
movement of particles from area of lower concentration to higher concentration (against concentration gradient)
not passive (requires energy from respiration)
active transport in root hairs
takes up water and mineral ions (healthy growth) from soil
minerals = higher conc in cell (no diffusion)
requires energy from respiration
Active transport in the gut
glucose & amino acids from food move from gut → bloodstream
required to move sugar to the blood against concentration gradient
What is the digestive system made up of?
Glands (salivary glands and the pancreas) = produce digestive juices containing enzymes
Stomach = produces hydrochloric acid to kill bacteria and to provide the optimum pH for the protease enzyme to work.
Small intestine = where soluble molecules are absorbed into the blood.
Liver = produces bile which is stored in the gall bladder, which helps with the digestion of lipids.
Large intestine = absorbs water from undigested food to produce faeces. This passes out of your body through the rectum and anus.
Enzyme
Biological catalyst (increases rate of reaction without being used up)
-present in many reactions (can be controlled)
-breaks up large molecules and joins small ones
-protein molecules (shape vital to function because each enzyme has uniquely shaped active site where substrate binds)
Enzyme optimum pH and temperature
Required because they are protein
-Optimum temp around 37 degrees (body temp)
-Optimum pH for most enzymes is 7, but some (produced in acidic conditions) have low optimum pH
Denaturing enzymes
TEMPERATURE:
-rate increases up to optimum but above it rapidly decreases and stops
-temp too hot = bonds break
-active site shape changes, so substrate can’t fit
PH:
-too high or low = forces holding amino acid chains that make up protein affected
-changes shape of active site, substrate can no longer fit in
Enzymes in digestion
Carbohydrases
Proteases
Lipases
Carbohydrases
Converts carbohydrates into simple sugars
e.g amylase breaks down starch into maltose
Produced in salivary glands, pancreas and small intestine (most starch eaten digested here)
Proteases
convert proteins into amino acids
e.g pepsin (produced in stomach but other forms can be found in pancreas and small intestine)
Lipases
convert lipids into fatty acids and glycerol
produced in pancreas and small intestine
Food tests
-Benedict’s test: sugars (turns brick red)
-Iodine test for starch (turns blue-black)
-Biuret test for protein (turns purple)
-Emulsion test for lipids (ethanol →cloudy layer)
or
-Sudan III test for lipids (red layer forms on top)
Where is Bile produced and stored and released?
Produced in liver
Stored in gallbladder
Released into the small intestine
Roles of bile
Alkaline: neutralise hydrochloric acid (comes from stomach). Enzymes have higher (more alkaline) optimum pH than those in stomach
Break down (emulsify) drops of fat. Large SA means lipase can chemically break down lipid →glycerol and fatty acids FASTER!
Role of circulatory system
Carries oxygen and nutrients to every cell in the body, removes waste products
How does the heart pump blood around the body?
In a double circulatory system (there are two circuits)
Deoxygenated blood flows into right atrium then into right ventricle - pumps it into the lungs to undergo gaseous exchange
Oxygenated blood flow into left atrium, then left ventricle - pumps oxygenated blood into the body
Heart - structure
-Muscular walls: strong heartbeat
-Left ventricle wall thicker: blood needs to be pumped all around body instead of just lung like right
-4 chambers: separate oxygenated and deoxygenated blood
-Valves: blood doesn’t flow backwards
-Coronary arteries: cover heart to provide its own oxygenated blood supply
Process of heart pumping blood
Blood flows into right atrium through vena cava and left atrium through pulmonary vein
Artia contract - blood into ventricles
Ventricles contract blood pushed into right ventricle into pulmonary artery - taken to lungs, left ventricle to aorta to be taken around body
Valves close to make sure blood doesn’t flow backwards
Natural resting heart rate
70bpm
controlled by group of cells in right atrium (pacemaker - provides stimulation through small electrical impulses which pass as a wave across the heart muscle, causing it to contract)
^ without this, heart wouldn’t pump fast enough to deliver required amount of oxygen
How can someone with an irregular heartbeat be helped?
Artificial pacemaker
Types of blood vessel
Arteries
Veins
CapillariesA
Arteries
Carry blood away away from the heart
-Layers of muscle in walls: make them strong
-Elastic fibres: allow them to stretch
-Helps vessels withstand high pressure created by heart pumping
Veins
Carry blood towards the heart
-Lumen (tube blood flows through): wide so allows low blood pressure to flow through
-Valves: ensure blood flows in right direction
Capillaries
Allow blood flow very close to cells → enable substances to move between them
-One cell thick: short diffusion pathway
-Permeable walls: substances can move across them
Gas exchange system
-Trachea (windpipe, air moves through here)
-Intercostal muscles (contract and relax to ventilate lungs)
-Bronchi (air from trachea move into these, lead to each lung)
-Bronchioles (bronchi split into these and air moves in)
-Alveoli (bronchioles lead to alveoli, air sacs where gaseous exchange occurs)
-Diaphragm (separates lungs from digestive organs, moves down causing inhalation)
Ventilation
Ribcage moves up + out, diaphragm moves down (volume of chest increases)
Increased volume = lower pressure
Air drawn into chest, air moves from areas of high →low pressure (environment to lungs)
Opposite happens when exhaling
Gas exchange
When inhale, alveoli fill with oxygen
Blood in capillaries surrounding alveoli is DEOXYGENATED (come from pulmonary vein) and has lots of carbon dioxide
Oxygen diffuses down conc gradient → capillary blood stream (low conc of oxygen)
Carbon dioxide diffuses down conc gradient from blood →Alveoli
How are alveoli adapted for gas exchange?
-Small, arranged in clusters (large SA for diffusion to take place over)
-Capillaries provide large blood supply, maintaining conc. gradient
-Walls of alveoli are very thing (short diffusion path)
What is blood made up of?
Plasma, red blood cells, white blood cells, platelets
Plasma
Liquid
Carries components in blood: red blood cells, white blood cells, platelets, glucose, amino acids, carbon dioxide, urea, hormones, proteins, antibodies, antitoxins
Red blood cells
Carry oxygen molecules from lungs to all cells in the body
Bioconcave disc shape: large SA
No nucleus: more room to carry oxygen
Contains red pigment haemoglobin, binds to oxygen and forms oxyhaemoglobin
White blood cells
Part of immune system (body’s defence against pathogens)
Have a nucleus
Different types:
1- Produce antibodies against microorganisms
2-Engulf and digest pathogens
3-Produce antitoxins to neutralise toxins/poisons produced by microorganisms
Platelets
Help blood clot form at site of wound
Clot dries and hardens - forms a scab which allows new skin to grow underneath while preventing microorganisms from entering
Small fragments of cells
No nucleus
Without - cuts result in excessive bleeding and bruising
Coronary heart disease
Occurs when coronary arteries that provide blood become blocked with the build up of fatty material.
Results in less blood flowing to heart - reduces oxygen supply
Non-communicable
May lead to a heart attack
Solutions to coronary heart disease
-Stents
-Statins
Note 
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