GCSE AQA BIOLOGY- TOPIC 1

What are all living things made up of?

cells

What is a eukaryotic cell?

complex, larger cells containing a nucleus and other organelles

What is a prokaryotic cell?

simple, smaller, single-celled (unicellular) organism with no nucleus and lacks other organelles

What subcellular structures are in plant and animal cells?

Nucleus

Cytoplasm

Cell membrane

Mitochondria

Ribosomes

What subcellular structures are only in plant cells?

Rigid cell wall

Permanent vacuole

Chloroplast

What subcellular structures are in bacteria cells?

Cell membrane

Cell wall

Cytoplasm

Plasmids

Circular strand of DNA

What is the role of a nucleus?

Contains genetic material that controls the activities of the cell

What is the role of the cytoplasm?

Gel like substance where most of the chemical reactions take place. it contains enzymes that control the reactions.

What is the role of the cell membrane

Holds the cell together and controls what goes in and out.

What is the role of mitochondria?

Where most of the reactions for AEROBIC respiration happen. Respiration transfers energy that cells need to work.

What is the role of ribosomes?

Where the proteins are made for photosynthesis.

What is the role of the cell wall?

its made of cellulose which supports and strengthens the cell

What is the role of the permanent vacuole?

it contains cell sap, a weak solution of sugar and salts

What is the role of chloroplasts?

Where photosynthesis occurs that makes food for the plant. It contains chlorophyll which absorbs the light needed for photosynthesis.

What is the role of plasmids?

Small circular rings of DNA, carrying some of the bacterium genes.

Why do we use microscopes?

They allow us to see things we cannot with the naked eye.

What is a light microscope?

A microscope that uses visible light and lenses to magnify the image. They are smaller and cheaper so are used in schools.

What is an electron microscope?

A microscope that uses electrons instead of light to form an image with a higher resolution and magnification. They allow us to see smaller structures such as ribosomes and plasmids, and the internal structures of mitochondria and chloroplasts. They are expensive so mainly used in labs.

Define the term resolution

The ability to distinguish between two points to create a sharper image.

What is the formula for magnification?

Magnification = image size / real size

Describe how to prepare a slide containing onion, to look under a light microscope.

Add a drop of water to the middle of a clean slide.

Cut up and onion and seperate it out into LAYERS.

Use TWEEZERS to peel off some EPIDERMAL TISSUE.

Add a drop of IODINE SOLUTION (a stain)- they highlight objects in a cell by adding COLOUR.

Place a cover slip (a square of thin transparent plastic or glass) on top. to do this....

Stand the cover slip UPRIGHT on the slide NEXT TO the water droplet. Carefully tilt and lower it so it covers the specimen. Try to not get air bubbles as it will obstruct the view of the specimen.

Features of a microscope

Eyepiece

Coarse adjustment knob

Fine adjustment knob

High and low power objective lenses

Stage

Light

How to look at your slide in a light microscope

Clip the SLIDE onto the STAGE

Select the LOWEST POWERED OBJECTIVE LENS- (lowest magnification)

Use the COARSE ADJUSTMENT KNOB to move the stage up to just below the objective lens

Look dow the EYEPIECE. use the coarse adjustment kob to move the stage down until it is ROUGHLY IN FOCUS.

Adjust the FOCUS with the FINE ADJUSTMENT KNOB until you get a CLEAR IMAGE of what is on the slide

to see with GREATER MAGNIFICATION- swap to a HIGHER POWERED OBJECTIVE LENS nad refocus.

Key point when drawing observations

sharp pencil

use at least half of the space

clear unbroken lines

NO colouring or shading

Subcellular structures should be drawn in proportion

Title

State magnification

Label important features

What is cell differentiation

The process in which cells become specialised for its job. they develop into different subcellular structures and turn into different types of cells to carry out specific functions

When and where does most cell differentiation occur?

Most differentiation occurs as an organism develops. In most ANIMAL cells, the ability to differentiate is LOST at an early stage AFTER they've become specialised. however PLANT cells DONT lose this ability.

How do sperm cells become specialised?

They become specialised for reproduction- the function of a sperm is to get the MALE DNA to the FEMALE DNA. it has a LONG TAIL and a STREAMLINED HEAD to help it swim to the EGG. there are lots of MITOCHONDRIA to provide ENERGY needed. it also carries ENZYMES in its head to digest through cell membrane.

What are nerve cells specialised for?

Rapid signalling. They carry ELECTRICAL SIGNALS from one part of the body to another. It contains LONG AXONS with BRANCHED DENDRITES to cover more distance and to connect to other nerve cells to form a NETWORK in the system.

What are muscle cells specialised for?

Muscle cells are specialised for CONTRACTION. they are LONG so they have space to contract and contain lots of MITOCHONDRIA to generate energy needed for contraction

What are root hair cells specialised for?

Absorbing WATER and MINERALS. root hair cells are on the surface of plant roots which grow into long HAIRS that stick out into soil. This gives it a LARGE SURFACE AREA for absorbing water and mineral ions from the soil

What are phloem and xylem cells specialised for?

Transporting substances such as FOOD and WATER around plants. to form the tubes the cells are long and joined end to end. Xylem cells are HOLLOW in the centre and PHLOEM cells have very few subcellular structures

What are chromosomes?

Coiled up lengths of DNA molecules. each chromosome carries a large number of genes. different genes control the development of different characteristics. eg hair colour.

What do body cells usually contain

Usually 2 COPIES of each chromosome- one from mother one from father.

How many chromosomes are there in gametes?

23. When they fuse together in reproduction to form an embryo, they contain 46 cells.

What is the cell cycle? 1 mark

The regular sequence of growth and division that cells undergo

What is the cell cycle explained?

GROWTH AND DNA REPLICATION STAGE:

in a cell that is not dividing it is spread out in long strings. before it divides it has to increase the amount of subcellular structures such as mitochondria and ribosomes. it then duplicates its DNA so there is 1 copy for each new cell. The DNA is copies and forms X shaped chromosomes. each arm is an exact dupliate

MITOSIS:

once copied the chromosomes line up at the centre of the cell and the fibres pull them apart. the two arms of each chromosome go to opposite ends of the cell. membranes form around set of chromosomes. These become the nuclei of the two new cells- the nucleus has divided. lastly the cytoplasm and cell membrane divide. the cells have now produced TWO NEW IDENTICAL DAUGHTER CELLS ALSO IDENTICAL TO PARENT.

What is the stage of the cycle called when the cell divided?

Mitosis

What is mitosis used for?

To grow and replace cells that have been damaged

what is the product of mitosis like?

results in two new cells identical to parent

What type of cells reproduce using binary fission?

Prokaryotic cells

What is the process of binary fission?

1. The circular DNA and plasmids replicate

2. the cells get bigger and the circular DNA strands move to opposite poles (ends) of the cell

3. the cytoplasm begins to divide and new cell walls begin to form

4. the cytoplasm divides and two daughter cells are produced. each daughter cell have 1 COPY of the circular DNA but can have a variable number of copies of plasmid(s)

What are the conditions for bacteria to divide in?

warm environment and lots of nutrients

How quick does bacteria such as Ecoli replicate?

as little as 20 minutes

What happens if become unfavourable for cell replication?

The cells stop dividing and begin to die

What is the mean division time?

The average amount of time it takes for one bacteria cell to divide into two

What is the equation for mean division time?

divide the total time by by the mean division time to get the number of divisons

What are bacteria and other microorganisms cultured in?

In a culture medium

What does a culture medium contain?

carbohydrates, minerals, proteins and vitamins that they need to grow

What substance can the culture medium be?

nutrient broth solution or solid agar jelly

What does the bacteria visible on the agar plate show?

colonies on the surface of the jelly or will spread out to give an even covering of bacteria

How to make and prepare an agar plate to see bacteria

Hot agar jelly is poured into a petri dish

when the jelly is set inoculating loops can be used to transfer microorganisms to the culture medium

alternatively a sterile dropping pipette can be used to get an even covering of bacteria

the microorganisms then multiply

Why is the temperature not kept above 25 degrees C in a school lab for culturing microorganisms?

harmful pathogens are more likely to grow at this temperature

What are the industrial conditions like for culturing microorganisms and why?

They are kept above 25 degrees C at much higher temperatures so they can grow faster

How to test the action of antibiotics (or antiseptics) on cultures of bacteria

1. Place paper discs soaked in different types (or concentrations) of antibiotics on an agar plate that has an even covering of bacteria. leave some space between the discs

2. The antibiotic should diffuse into the agar jelly. Antibiotic resistant bacteria will continue to grow on the agar around the paper discs but non resistant strains will die. a clear area will be left where the bacteria have died called an INHIBITION ZONE

3. make sure you use a control- paper disc that is not soaked in antibiotic. soak in sterile water to be sure of a difference between the growth of the bacteria around the control and around the one of the antibiotic discs.

4. leave the plate for 48 hours at 25 degrees C

5. the more effective bacteria will have a larger inhibition zone.

What will contamination by unwanted organisms do when culturing microorganisms?

Potentially lead to the growth of pathogens, affecting the results

How to reduce the risk of pathogens when culturing microorganisms

-sterilise the petri dish and culture medium by heating before use to kill unwanted microorganisms lurking on the dish.

-sterilise the inoculating loop in a hot flame on a bunsen

-after heating petri dish lid should be taped on lightly to stop microorganisms from the air getting in

-store petri dish upside down to stop condensation water droplets falling on agar surface

What is a pathogen?

Microorganisms that cause disease

equation for calculating the area of the inhibition zone

Area = pi x r squared

What is differentionation

the process by which a cell changed to become specialised for a job

what is the other term for stem cells

undifferentiated cells

what to undifferentiated (specialised cells) divide to produce

more undifferentiated stem cells.

what can stem cells differentate into

different types of cells depending on the 'instructions' they are given

Where are stem cells found?

In early human embryos or the bone marrow of adults

What can adult stem cell differentiate into?

cannot turn into any type of cell. only certain ones such as red blood cells

what are stem cells and embryonic cells grown in a lab to produce?

clones (genetically identical cells) and are made to differentiate into specialised cells to use in medicine or research.

What are stem cells already used in?

medicines to cure diseases. for example stem cells are transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient

What could embryonic stem cells be used for?

replace faulty cells in sick people- could make insulin producing cells for people with diabetes, nerve cells, for people paralysed by spinal injury.

What happens in therapeutic cloning?

An embryo is produced with the same genes as the patient so that the stem cells from the embryo are not rejected by the patient's body so they may be used for medical treatment.

what is the risk involved when using stem cells in medicine?

they may become contaminated with a virus which could be passed on to patient to make them sicker.

Why would people be against stem cell research?

- they feel that embryos shouldnt be used for experiments as they are a potential human life

-curing existing patients that are suffering is more important that the rights of embryos

- embryos used in research are unwanted ones from fertility clinics which if not used for research would be destroyed

- campaigners feel that scientists should concentrate more on finding and developing other sources of stem cells so that people can be helped without using embryos

- some countries stem cell research is banned. in the uk its ok under strict guideline

where are stem cells in plants found?

in the meristems- parts where growth occurs

when and what can a meristem differentiate into?

throughout the plants entire life it can differentiate into any type of plant cell

what can the stem cells in plants be used for?

To produce clones of plants quickly and economically

what are stem cells in plants used to grow?

more plants of rare species to prevent extinction

what is an advantage of stem cells in plants?

they can be used to grow identical plants that have desired features for farmers for example disease resistance.

What is the definition of diffusion?

the net movement of particles from an area of high concentration to an area of low concentration to make it evenly spaced

what states of matter does diffusion occur in?

liquids and gases

How does concentration affect the rate of diffusion?

the bigger the concentration gradient the faster the diffusion rate

How and why does temperature have an affect on the rate of diffusion?

The higher the temperature the faster the rate of diffusion because the particles have more energy to move faster

what is the role of cell membranes in diffusion

allows small molecules such as oxygen, glucose, amino acids and water to diffuse through the membranes for respiration

how does the surface area of a cell membrane affect the rate of diffusion?

the larger the surface area the faster the diffusion rate because more particles can pass through at once

What is the definition of osmosis?

The movement of water molecules from a higher water concentration to a lower water concentration ACROSS A PARTIALLY PERMEABLE MEMBRANE

What is a partially permeable membrane?

A membrane that has very small holes that only small molecules such as water can pass through them and bigger molecules such as sugar (sucrose) molecules cant.

which direction do water molecules pass through during osmosis?

both ways through the membrane- because the water molecules move randomly all the time

Why is there a steady net flow of water molecules in osmosis?

because there are more water molecules on one side than the other there is a steady net flow of water in the region with fewer water molecules - ie into the stronger sugar solution

this means that the stronger sugar solution gets more dilute as the water is trying to 'even up' the concentration either side

How to observe the effect of the sugar solutions on plant tissue

1. cut up a potato into indentical cylinders and get beakers with different sugar solutions in. one should be pure water and one should be very concentrated.

2. measure the mass of the cylinders then leave for 24 hours

3. take them out and dry with a paper towel and measure the mass again

4. if water how been drawn in the mass will have increased. if water has been drawn out the mass would have decreased. calculate the percentage change in mass then plot a graph

the dependant variable is the chip mass and the independent variable is the concentration of the sugar solution. all the other variables (volume of solution, temperature, time, type of sugar used) must be kept the same

errors- a. carrying out the method (if some potato cylinderss were not fully dried the excess water would give a higher mass, or if the water evaporated from the beakers, the concentrations of the sugar solutions would change).

You can reduce the effect of these errors by repeating the experiment and calculating a mean percentage change at each concentration

what is active transport?

movement of molecules into or out of a cell against a concentration gradient- from a low to high concentration

describe the structure of a root hair cell and why

grows hairs that stick out into the soil

each branch of a root will be covered in millions of hairs

this gives the plant a large surface area for absorbing water and mineral ions from the soil

plants need these mineral ions for healthy growth

the concentration of minerals is usually higher in root hair cells than in the soil around them

so the root hair cells cannot use diffusion to take up minerals

The process of active transport

active transport requires ENERGY from respiration to make it work. allows the plant to absorb minerals from a very dilute solution against the concentration gradient. it also happens in humans for example taking in glucose from the gut and kidney tubules

active transport in humans process

active transport is used in the gut when there is a lower concentration of nutrients in the gut but a higher concentration of nutrients in the blood

1. when there is a higher concentration of glucose and amino acids in the gut they diffuse naturally into the blood

2. BUT sometimes there is a lower concentration of the nutrients in the gut than there is in the blood

3. this means the concentration gradient is the wrong way.

4. allows nutrients to be taken into the blood

5. this means glucose can be taken into the bloodstream when its concentration in the blood is already higher than the gut. its then transported to cells for respiration

what is an exchange surface

A part of an organism over which substances are exchanged with the environment depending on its surface area to volume ratio

examples of how organisms exchange substances with the environment

oxygen and carbon dioxide are transferred between cells and the environment during gas exchange

in humans urea diffuses from cells into the blood plasma for removal from the body by the kidneys

why do single celled organisms diffuse directly into the cell

they have a large surface area compared to their volume so enough substances can be exchanged across the membrane to supply the volume of the cell

why do multicellular organisms have a smaller surface area compared to their volume?

not enough substances can diffuse from their outside surface to supply their entire volume. they need some sort of exchange surface for efficient diffusion

How are exchange surfaces adapted to maximise effectiveness?

they have a thin membrane so substances only have a short distance to diffuse

they have a large surface area so lots of substances can diffuse at once

exchange surfaces in animals have lots of blood vessels to get suff in and out of the cells quickly

gas exchange surfaces in plants and animals are ventilated too so air can move in and out

how does gas exchange happen in the lungs

lungs trafers oxygen to the blood and to remove waste carbon dioxide from it.

the lungs contain little air sacs called alveoli where gas exchange takes place

How are alveoli adapted for gas exchange?

large surface area

good blood supply

thin walls - short diffusion pathway

moist lining for dissolving gasses

How are villi adapted for absorption?

thin walls- single layer of surface cells

large surface area

good blood supply close to the surface to assist absorption

where are the villi located

in the small intestine

what gas diffuses into the airspaces within the leaf where photosynthesis occurs

carbon dioxide