Cells and Pathogens

Microscopes

Magnification: how much bigger an image is

e.g. x2 = two times bigger

To work it out you multiply the magnification of the two lenses. For example if the objective lens is x5 and the eyepiece lens is x10 the magnification is x50

Resolution: how detailed the image is

It is the smallest distance between two points where they can still be seen as separate

e.g. with a resolution of 4mm points 4mm apart would be seen as separate, but any closer they would become one.

Field of view: the circular area in a microscope

Scale bars can be used to estimate sizes

Magnification = image actual

An electron microscope is a type of microscope that uses beams of electrons as a source of illumination and can see much smaller things than a light microscope

Units

To get from each unit to the one below it you divide by 1,000

Plant and Animal Cells

Eukaryotic cell: a cell with a nucleus

Parts of an animal cell

Cell membrane: thin bag, controls what enters or leaves

Cytoplasm: watery jelly, cell’s activities occur there

Mitochondria: aerobic respiration occurs here

Nucleus: controls the cell, contains chromosomes and DNA

Ribosome: makes new proteins

Additional parts of a plant cell

(plant cells have all the parts of an animal cell but also these ones)

Cell wall: supports and protects cell, made of cellulose

Chloroplast: contains chlorophyll, used for photosynthesis

Vacuole: stores cell sap which keeps the cell firm and rigid

Specialised Cells

Specialised cells have a function (job). Their sizes, shapes and sub-cellular structures have adapted to their functions.

Specialised cells for digestion have membranes with tiny folds called microvilli which increase the surface area of the cell, allowing for faster absorption.

Specialised cells for reproduction (aka egg cells and sperm cells) fuse to create a singe cell, so each only have one set of chromosomes (all cells need two) so that they can join to create a full cell.

Sperm cells also have adapted by having a streamlined shape, lots of mitochondria for energy, a tail for swimming and an acrosome (a cap-like structure that helps them burrow into into the egg cell).

Egg cells have adapted by having nutrients in their cytoplasm and being able to change the cell membrane after fertilisation to stop more sperms coming in.

Diploid cells: cells with two sets of chromosomes

Haploid cells: cells with one set of chromosomes

Bacteria

Bacteria are prokaryotic (single celled) organisms. They are smaller than other cells.

Bacteria have a flagellum, which spins around to move the cell.

They are also prokaryotic, meaning they have no nucleus, chromosomes, mitochondria or chloroplasts. Instead they contain chromosomal DNA, which controls the cell’s activities

Extra features of bacteria

Flagellum: spins around to move the cell

Slime coat (not on all bacteria): for protection

Flexible cell wall: for support, not made of cellulose

Plasmid & Chromosomal DNA: controls the cells activities in place of the nucleus

Pathogens

Pathogens are disease-causing organisms

All kinds of organisms can be infected by microorganisms e.g. plants can be infected by fungi

Viruses aren’t true organisms, as they don’t have cellular structure. They infect a cell and take over its DNA to make new viruses.

Some bacteria are essential for health, but some don’t effect us. People can have diseases in them and never show symptoms.

Spreading pathogens

Pathogens are spread in many different ways

Some infections cause people to sneeze/cough, sending droplets containing pathogens into the air.

Fungi spreads through the air in spores carried by the wind

Some pathogens spread in water.

Pathogens of the digestive system can spread in food

Oral route: when a pathogen enters through the mouth

Viruses

Capsids: strands of genetic material surrounded by a protein coat. All viruses have these.

Viruses can’t replicate on their own - they have to enter a cell and take over its processes.

The cell copies the viral genetic material and makes new components (genetic material & proteins) which assemble into new viruses. This damages the cell, causing disease

Lysis: complete breakdown of the cell

Lytic pathway: the life cycle of a virus that causes lysis

Lysogenic pathway: the life cycle of a virus that inserts genetic material into a cell

Lytic cycle

1. Virus attaches to cell and inserts genetic material
2. New genetic material and proteins are created and assembled
3. Cell lyses (breaks down), releasing the viruses
4. Repeat!

Lysogenic cycle

1. Genetic material of virus inserts into bacterial chromosome
2. Bacteria reproduces, replicating viral genetic material with it (this can happen lots of times)
3. Genetic material separates from bacterial chromosome
4. Repeat!

The lysogenic cycle doesn’t cause the lysis of the cell

Testing foods

Health and disease

Health definition: a state of complete physical, mental and social well being and not just the absence of disease

To be healthy your cells need to be able to function, disease occurs when this can’t happen

Symptoms give you cues as to which cells/organs are affected

Treatments will target diseased cells

Communicable diseases are diseases caused by pathogens

Non-communicable diseases are diseases that can’t be spread from one person to another e.g. heart attacks, cancer, diabetes

Pathogens are organisms that make other organisms ill. They do this by producing toxins that damage the cells or invade them and change their functions.

Pathogens fall into four groups:

viruses: hiv, ebola, influenza

bacteria: helicobacter, vibrio cholerae

fungi: chalara ash dieback

protists: malaria

Pathogens are:

• living organisms
• tiny
• made of cells that damage others
• cause disease

Cells

Cells are the smallest units of life, and carry out life processes. All organisms are made of cells.

Bacteria are prokaryotic (single celled) organisms. They are smaller than other cells.

Eukaryotic cells: cells that have DNA in their nucleus (animal and plant cells). They also contain other organelles e.g. mitochondria and chloroplasts

Diseases

Cholera

type of pathogen: bacteria

nature of disease: diarrhoea

how it’s spread: water

how to prevent: wash hands cook food, clean water

Tuberculosis

type of pathogen: bacteria

nature of disease: lung damage

how it’s spread: airborne

how to prevent: wearing masks, good ventalation

Chalara ash dieback

type of pathogen: fungus

nature of disease: leaf loss, bark lesions

how it’s spread: airborne

how to prevent: destroying infected plants

Malaria

type of pathogen: protist

nature of disease: damage to blood and liver

how it’s spread: animal vectors

how to prevent: insect repellent, long sleeves mosquito nets

HIV

type of pathogen: virus

nature of disease: destroyed white blood cells, leading to weakened immune system and AIDS

how it’s spread: body fluids

how to prevent: safe sex, blood testing

Helicobacter pylori

type of pathogen: virus

nature of disease: stomach ulcers

how it’s spread: oral transmission

how to prevent: cooked food

Ebola

type of pathogen: virus

nature of disease: haemorrhagic fever

how it’s spread: body fluids

how to prevent: don’t touch bodies, isolate

Chlamydia

type of pathogen: bacteria

nature of disease: pain while peeing, unusual discharge

how it’s spread: unprotected sex

how to prevent: get tested, get treated

Biomolecules

Monomer: building block of a substance

Food is a source of biomolecules. There are three types:

Enzymes

Enzymes speed up processes without being used up themselves

Denature: when a protein changes shape due to extreme temp/pH. It needs to be a certain shape to work, so then it can’t work

Active site: where the enzyme and the substrate join

Specifity: one type of enzyme for one type of substrate (as they need to fit together)

Complimentary: the enzyme & substrate fit together (they’re the opposite shape)

Substrate: what is broken down (made out of bonded glucose and fructose). Biomolecules

Product: the result(s) of the reaction

Enzyme-substrate complex: the structure formed when the enzyme and the substrate come together

Catalyst: something that speeds up a reaction without being used up (e.g. an enzyme)

Catalyses: speeds up

Enzymes end in ‘ase’ e.g. amylase, lipase, protease

Enzyme activity increases as you increase the temperature, until it reaches its optimum (where it will work the fastest), after which it denatures and doesn’t work at all any more

How enzymes work

1. The substrate binds to the enzyme forming an enzyme-substrate complex
2. Stress is placed on the bonds in the substrate and they break
3. Products are released and the enzyme can bind other substances

Rate and Graphs

Rate of reaction: relative speed at which reaction it takes place

Measured in 1/time taken to reach end point, units are s^-1

It can be plotted on a graph with rate on the y axis (vertical) and substrate concentration on the x axis (horizontal)

All of these graphs are reversed if you put time take to dissolve instead of rate

Dependent variable: what you measure: on y axis

Independent variable: what you change: on x axis

DNA

Base pairs:

A binds with T

D binds with G

A is complimentary to T and D is complimentary to C

You need a base, a sugar and a phosphate - all these together are called a nucleotide

DNA molecules twist and have a double helix shape (double: two strands, helix: twisted)

A section of a DNA molecule is called a gene, and all the genes in a cell form a genome

DNA is found in the nucleus

Extracting DNA:

To extract DNA you first need to break the cells open to get to it (by mashing it)

Then you filter the debris e.g. the cell walls out and collect the nuclei

Add soapy water to dissolve the cell membranes and the nuclear membrane, which are made of lipids

Use ice cold ethanol to extract the DNA, you will get some slimy stuff which is the DNA

B strands are linked by a series of complementary base pairs joined together by weak hydrogen bonds

C nucleotides consist of a sugar and a phosphate with one of four different bases attached to the sugar

Cellular respiration & transport

Cellular respiration

Cellular respiration is a series of chemical reactions that take place continually in all cells. During the process glucose is broken down releasing large amount of energy. It is an exothermic reaction (energy is released in heat) so it also keeps animals warm. Some of the energy released is used to synthesise ATPs

ATP: a short term energy storage molecule used for metabolism

Aerobic respiration requires oxygen to break down the glucose and forms carbon dioxide and water

glucose + oxygen → carbon dioxide + water (+ energy)

In eukaryotic cells (plants and animals) aerobic respiration happens in the mitochondria. Bacterial cells don’t have mitochondria, so it happens in their cytoplasm.

Muscle cells can also respire without oxygen in anaerobic respiration. It doesn’t produce as much energy, however, and produces toxic waste - lactic acid. It also creates an oxygen debt; eventually oxygen is required to break down the lactic acid.

glucose → lactic acid (+ energy)

Calorimeters

Stirrer: for mixing the water to make sure heat is evenly distributed

Lid: makes sure water doesn’t evaporate

Pure oxygen supply: burns food fully

Water jacket: heats water evenly & fully

Insulating jacket: makes sure no heat is lost to the surroundings

Thermometer: for measuring the temperature of water

Magnifying eyepiece (on thermometer): so you can see exactly what temperature the water is

Lots of water: so the heat doesn’t get too high and the water evaporates

Energy in food practical

1. Temperature of water measured
2. Mass of water measured
3. Mass of food measured
4. Food is ignited with electricity
5. Heat transfers to the water
6. Temperature of water measured again

Energy transferred = mass of water x 4.2 x temperature increase mass of food

Diffusion

Diffusion: particles moving from high to low concentration because of kinetic energy

Kinetic energy: the energy that allows particles to move

Factors that effect diffusion:

• Concentration (number of particles)
• Temperature (effects kinetic energy)
• Type of particle (density, mass, radius)
• Diffusion distance (the further the particles have to diffuse, the longer it takes)

Examples of diffusion:

• Lungs: oxygen diffusing from alveoli into blood in respiration
• Small intestine: glucose into blood
• Cells: oxygen from blood into mitochondria

Rate of diffusion = surface area x concentration difference thickness of membrane

(this is called Fick's law)

Concentration difference = mass of solute
volume of solution

Osmosis

Aqueous solution: water based solution

When two aqueous solutions of different concentrations are separated by a semi-permeable membrane (/selectively permeable membrane) a water potential gradient is established

Water will move from the high water potential (dilute) solution to the low water potential (concentrated) solution in osmosis

The water still uses kinetic energy to move

Osmosis in potatoes practical

1. Use 5 concentrations of sucrose and 5 potato slices cut to the same size
2. Weigh each potato slice and record the mass
3. Measure each potato slice and record the length
4. Put each slice in a different solution of sucrose
5. After 25 minutes take them out and record the new mass and length
6. You can also calculate the percentage change in weight an mass:

Percentage change

Helps compare different results when there are different starting measurements

Percentage change = final mass - initial mass x 100 initial mass

Active transport

Active transport is moving specific molecules against the concentration gradient (from low to high concentration). It requires energy in the form of an ATP (from respiration).

Cells that do this need special transport proteins in their membranes and lots of mitochondria.

The molecules are moved through a semi-permeable cell membrane

Active transport helps the growth and respiration of cells. Organisms need transport systems to be able to get all the substances needed in cells to the right place.

Surface area : volume ratio

24cm² : 8 cm³ = 3:1

• Surface area in cm²
• Volume in cm³
• No units when simplified

Alveoli & lungs

Adaptions