GCSE Biology B1: Cell Biology

Eukaryotic Cells (7)

- Plant and Animal cells

- Cell membrane

- cytoplasm

- nucleus containing DNA

- ribosomes

- mitochondria

- chloroplasts

Prokaryotic Cells (7)

- Bacterial Cells

- much smaller

- cell wall

- cell membrane

- cytoplasm

- singular circular strand of DNA

- plasmids

prefixes:

- centi

- milli

- micro

- nano

0. 01

0. 001

0. 00,001

0. 000,000,001

nucleus

- Contains genetic material

cytoplasm (3)

- where most chemical reactions occur

- contains enzymes

- organelles are found in it

ribosomes (2)

- protein synthesis occurs here

- found on a structure called the rough endoplasmic reticulum

cell membrane

- controls the substances going in and out of the cell

cell wall

- contains cellulose to give the cell structure

chloroplasts

- contains chlorophyll, which absorbs light for photosynthesis to make food for plants

permanent vacuole (2)

- contains cell sap

- improves cell rigidity

mitochondria

energy is released via aerobic respiration here

sperm cell (4)

- to carry male DNA to the egg for reproduction (combining male and female DNA)

- steamlined head and long tail (flagellum) to aid swimming

- many mitochondria where respiration to supply energy for the cell to move

- acrosome (top of the head) has digestive enzymes which break down the outer layers of membrane of the egg cell

Nerve cells (4)

- to transmit electrical signals quickly from one place in the body to another

- long axon to enable impulses to be carried along long distances

- having lots of extensions frrom the dendrites means branched connections can form with other nerve cells

- nerve endings have many mitochondria which supply the energy to make neurotransmitters. these allows the impulse to be passed from one cell to another

Muscle cells (4)

- contract quickly to move bones or to squeeze for movement

- special proteins slide over each other, causing the muscle to contract

- lots of mitochondria to provide energy from respiration for contraction

- they can store glycogen that is used in respiration by mitochondria

Root hair cells (4)

- to take up water by osmosis and mineral ions by active transport from the soil as they found in the tips of roots

- have large surface area due to root hairs, meaning more water can move in

- 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

Xylem cells (3)

- to transport water and mineral ions up the plant from the roots to the shoots

- 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 continious 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

phloem cells

- to carry the products of photosynthesis to all parts of the plants

- cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell

- the energy these cells need to be alive is supplied by mitochondria of companion cells

cell differentiation

- stem cells undergo diffrentiation to form specialised cells and they can make more from mitosis.

- they switch their genes on and off to produe different proteins to aquire different sub-cellular substances

light microscope vs electron miscroscope

- 2000 magnification so can only see bacteria and large organelles

- 2 000 000 magnification and can see individual sub cellular structures

how to calculate magnification

- magnification of eye piece lens x magnification of the objective lens

how to calculate the size of the object

size of image/magnification (I = AM)

culturing microorganisms (2)

- bacteria multiply via binary fission which can be as quick as every 20minutes

- it has carbs for energy, minerals, proteins and vitamins

where can grow microorganisms in a lab

- in a nutrient broth solution: making a suspension of bacteria to be grown and mixing wih sterile nutrient broth, stoppering the flask with cotton wool to prevent ai from contaminating it and shaking regularly to provide oxygen for the growing bacteria

- agar gel plate: the agar acts as a culture medium and bacteria grownm on it forms colonies on the surface

hot sterilised agar jelly is poured into a sterilised petri dish which is left to cool and set. inoculating loops are dipped in a solution of the mciroorganism and spread over the agar evenly. a lid is taped on and the plate is incubated for a few days so the microorganisms can grow (stored upside down)

why does the petri dish and culture media need to be sterilised before use (2)

- autoclave oven or UV light

- they will be contaminated with other microorganisms and compete for nutrients and space or they can produce a new pathogen

why should the lid of the petri dish not be completely shut tight (2)

- sealing stops airborne microorganisms from contaminating the ulture

- however it can result in harmful anaerobic bacteria growing

why the culture need to be incubated at 25 degrees (2)

- if it is incubated at higher temperatures, near 37 degrees it would be more likely that bacteria could be harmful to humans as they are able to grow at human body temp which is their optimum temp.

- at lower temperatures they would not be able to grow

how to calculate number of bacteria in a population

number of bacteria at the start x 2^number of divisions

how to calculate the number of divisions

time the population is left for/ mean division time

how to test the effectiveness of antibiotics and dissinfectants (4)

- soak the paper discs in different types of antibiotics and place on an agar plate evenly spread with bacteria

- one disc should be a control, soaked in steriled water

- leave the plate at 25 degrees for 2 days

- the bigger the zone of inhibition the more effective the antibiotic is

how many chromosomes do you have

46

mitosis

interphase: the cell grows, organelles grow and increase in number , the protein synthesis occurs and DNA is replicated and e4nergy stores increase

Mitosis: chromosomes line up at the equator of the cell and the cell fibres of each chromosome is pulled to either side of the cell. the nucleus reforms

Cytokinesis: two identical daughter cells form when the cytoplasm and cell membranes divide

why is cell division good (2)

- for development and growth and replacing damaged cells

- and do reprouce asexually

embryonic stem cells (3)

- when an egg and sperm cell fuse to form a zygote

- scientists can clone these cells and culture them and direct them to differentiate into almost any cell in the body

- they can replace insulin producing cells in people suffering from diabetes or nerve cells for those who are paralysed with spinal cord injuries

adult stem cells (3)

- found in roots and shoots tips

- differentiate into any type of plant and have this ability throughout the life of the plant

-they can use this to produce clones in the plant in case of extinction or they develop a certain disease

therapeutic cloning (4)

- embryo being produced with the same genes as the patient

- these can be harvested to obtain embryonic stem cells

- these could be grown into any cell the patient needs such as new tissues or organs

- these would not be rejected as they have the same geneti make-up as the individual

benefits of research with stem cells

- can be used to replace damaged or diseased body parts

- unwanted embryos from fertility clinics can be used as they would be discarded anyways

-research into the process of differentiation

problems with research of stem cells

- we dont completely undertsand the process of differentiation so it is hard to control stem cells to form the cells we want

- removal of stem cells destroys the embryo so people think its unethical

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 con to an area of lower conc

no energy is required

what molecules can't move across in diffusion

oxygen, glucose, amino acids, water, starch, proteins

factors that affect the rate of diffusion (3)

- concentration gradient: the greater the difference in conc the faster the rate of diffusion. this is because more particles are randomly moving down the gradient than are moving against it

- temperature: the greater the temperature, the greater the movement of particles, resulting in more collisions and therefore a faster rate of diffusion

- surface area of the membrane: the greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion

single-celled organisms with diffusion

- can diffuse to trandsport molecules into their body from the air as they have a large surface area to volume ratio. due to low metabolic demands diffusion across the surface of the organism is sufficient enough to meet its needs

multicellular organisms with difusion

surface area to volume ratio is small so they can't rely on diffusion alone so instead surfaces and organ systems have a number of adaptations that allows molecules to be transported in and out of cells

adaptations for diffusion

- large surface area: the more particles can move through, resulting in faster rate of diffusion

e.g. lungs, small intestine, fish gills, leaves

- having a thin membrane: provides a short diffusion pathway, allowing the process to occur faster

e.g. lungs and small intestine

- having an effiicient blood supply/being ventilated (in animals): creates a steep concentration gradient so diffusion occurs faster

e.g. lungs, fish

osmosis

- the movement of water from a less concentration solution to a more concentrated one through a partially permeable membrane.

no energy is needed

osmosis in plants (2)

- if external solution is more dilute, water will move into the cell and into the vacuole causing it to swell (turgor) which is essential for keeping the leaves and stems rigid

- if external is less dilute then the water will move out of the cell and become soft. Eventually the cell membrane will move away from the cell wall (plasmolysis) and it will die

Osmosis RP

- placing potato tubers in different conc of sugar solutions results in different volumes of water moving in and out of the tubers. This affects its mass. By measureing the mass of the tuber before and after placing it in the solution we can see whether the conc of external solution or potato was higher, epending on whether it is heavier or lighter. Calc percentage change in mass and plot on a graph

active transport

movement of particles from an area of low conc to high conc against the conc gradient. requires energy from respiration

active transport in root hairs (3)

- they take up water and mineral ions for healthy growth from the soil

- mineral ions are usually in higher conentrations in the cells, meaning diffusion can not take place

- requires energy from respiration to work

active transport in the gut (3)

- substances such as glucose and amino acids from your food have to move from your gut into your bloodstream

- sometimes there can be a lower conc of sugar molecules in the gut than the blood meaning diffusion can't take place

- active transport is required to move the sugar to the blood against its conc gradient

diffusion in the lungs

-oxygen is transferred to the blood and co2 is transferred to the lungs. This takes place across the surface of millions of alveoli which are covered in tiny cappilaries which supply blood

diffsion in fish (3)

- the gills where gas exchange takes place. water which has oxygen passes through the mouth and over the gills

- each gill has plates called gill filaments and gill lamellae which is where diffusion of oxygen into the blood and diffusion of co2 into the water takes place

- blood flows in one direction while water flows in the other