GCSE Edexcel Biology Paper 1 Comb High.

What are the two types of cells?

Prokaryotic (single celled), smaller and simpler

Eukaryotic (Animal and Plant) larger, complex.

Nucleus

Contains genetic material that controls the activities of the cell which is arranged into chromosomes.

Cytoplasm

Gel-like substance where most chemical reactions occur

Contains enzymes which control these reactions.

Cell membrane

Holds the cell together and controls what goes in and out

Mitochondria

This is where most chemical reactions for respiration takes place

Respiration transfers energy needed for the cell to work.

Ribosomes

Translation of genetic material in the synthesis of protein

Large Vacuole

It maintains internal pressure

Contains cell sap, a weak solution of sugars and salts.

Chloroplasts

Site of photosynthesis and contains green substance known as chlorophyll

Chromosomal DNA

Controls the cell's activities and replication.

It floats free in the cytoplasm.

One long circular chromosomes

Plasmid DNA

Separate from circular DNA

Can replicate independently for drug resistance

Flagellum

A long, hairlike structure that grows out of a cell and enables the cell to move.

Can move closer to beneficial substances like oxygen or nutrients and away from harmful toxins.

What are specialised cells?

Cells that are adapted to a specific function.

In sexual reproduction, how and what happens between the sperm cell and the egg cell?

Egg cell fuses with the sperm cell to create a fertilised egg then becoming an embryo, egg cell has 23 chromosomes and sperm cell has 23 chromosomes creating the required 46 when they fuse.

Haploid cell

Having half the chromosomes as a normal body cell.

How is an egg cell adapted to it function?

Carries female DNA

Has nutrients in cytoplasm able to nourish the embryo

Haploid

Straight after fertilisation the membrane changes structure preventing any other sperm cell from getting in, ensuring that the offspring receives the right amount of DNA.

How is a sperm cell adapted to its function?

Tail to be able to swim

Mitochondria in the middle to be able to cover the long swim

Enzymes in acrosome to digest the membrane of egg

Haploid

What do ciliated epithelial cells do?

Lines the surface of organs

Some have cilia (hair like) on top of the surfaces of the cell

move substances along the surface of the tissue.

lining of airways contains lots of ciliated epithelial cells, helping move mucus up the throat so it can be swallowed and not reaching the lungs

What do microscopes do?

magnify images which allows us to see what we could not with the naked eye.

increases resolution- the ability to distinguish between two points.

Explain the light microscope.

Invented in 1590's

Passes light through specimen

Allow us to see nuclei and chloroplasts

Living cells can be seen

Explain the electron microscope

uses beams of electrons to pass through the specimen

cells must be killed

higher resolution and magnification

How to view a specimen using a light microscope

-thin slice of specimen

-clean slide, pippette to put drop of water on it to secure specimen

-put the specimen using tweezers

-add a drop of stain like iodine if you specimen is colourless/transparent

-cover slip placed on carefully ensuring no air bubbles

-lowest powered lens

-adjust using fine adjustment knob til clear image

how to measure FOV

take ruler and place on stage

look down the eyepiece lens and measure the diameter of the circular area that you can see

As mag increases the FOV decreases

How to create a scientific drawing of a specimen

use a sharp pencil

draw clear lines

take up half the space

label

include the mag used

How to work out total magnification

total magnification = eyepiece lens magnification x objective lens magnification

How to work out magnification of an image?

Image size= actual size x magnification

How to convert between mm, ym, nm, pm?

x10m millimetre

x10-3m micrometre

x10-6m nanometre go smaller divide 1000

x10-9m picometre go bigger times 1000

What are chemical reactions?

makes you work, 1000s going on at all time.

very specific to get the right amount of substances

Why can't we just speed up chemical reactions by increasing temperature?

Increasing temperature speeds up all reactions which also means the bad/unwanted reactions.

What are enzymes?

Enzymes are biological catalysts that speed up chemical reactions without being changed or used up.

How do enzymes work?

All enzymes have active sites- the part where it joins onto its substrate to catalyse a reaction.

Very specific and will not work if doesn't fit

Name three factors that affect the rate of reaction.

Temperature, PH and Substrate Concentration

Explain how temperature affects enzyme activity

- Enzymes work faster as the temperature increases but become denatured after a certain temperature (around 40C)

- Denaturing occurs when the active site changes shape due to change of temp as the substrate no longer fits the active site

Explain how pH affects enzyme activity.

Enzymes have an optimum pH level where there is the highest activity, once past that it denatures, meaning the bonds change and the structure of the enzyme is altered.

Explain how substrate concentration affects the rate of reaction

the higher the substrate concentration, the faster the reaction.

because there is more substrates so its more likely enzymes to meet up and react with each other.

only true up a point because eventually there will all be full.

What is an example of an chemical reaction that can be used to investigate how PH affects Enzyme

The enzymes amylase catalyses the breakdown of starch to maltose. If starch is present, the iodine solution will change from browny-orange to blue-black.

how to investigate the effect of pH on enzyme activity

-put a drop of iodine solution into every well of the spotting tile

-place a bunsen burner on a heat-proof mat, and a tripod and gauze over the bunsen burner

-put a beaker of water on top of the tripod ad heat the water until 35C (using a thermometer)

-add 3cm3 of amylase solution and 1cm3 of a buffer solution with a PH of 5 to a boiling tube

-Using test tube holders, put the boiling tube into a beaker of water and wait for 5 minutes

-Use a different syringe to add 3cm3 of starch solution to the boiling tube

-Mix the contents of the boiling tube and start a stop clock.

-Use continuous sampling to record how long it takes for the amylase to break down the starch.

-Use a dropping pipette to take a fresh sample from the boiling tube every ten seconds and drop it into a well. If iodine stays browny orange, starch is no longer present.

-Repeat the whole experiment with different PH to see how it affects the time taken for the starch to be broken down.

-Remember to control any variables each time

How to calculate the rate of reaction?

Rate = 1000/time

Rate of reaction=change/time

How do organisms break down big molecules to allow them to be used in the body?

After enzymes break carbohydrates, protein and lipids down they can pass easily through the walls of the digestive system allowing them to absorbed into the bloodstream, at this size they can pass through cells.

How do plants store and then use the energy?

Plants store energy in the form in the form of starch (a carbohydrate). When plants need energy, enzymes break down the starch into smaller molecules (sugars) ready to be respired to transfer energy to be used by the cells.

What converts carbohydrates into simple sugars?

Carbohydrates get broken down into simple sugars by carbohydrases. Example in picture

What converts proteins into amino acids?

protease converts protein into amino acids

What converts lipids into glycerol and fatty acids?

Lipase converts lipids into glycerol and fatty acids

How can enzymes synthesise carbohydrates, lipids and protein from their smaller components?

Carbohydrates can be synthesised by using simple sugars.

Protein are made by joining amino acids.

Lipids from fatty acids and glycerol.

What is diffusion?

Diffusion is the movement of particles from an area of higher concentration to lower concentration.

Occurs in both liquid and gases because they both are free to move.

Only small molecules can diffuse through cell membrane like glucose, amino acids, water and oxygen.

Doesn't require energy

What is osmosis?

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of lower water concentration.

A partially permeable membrane is one with very small holes in it, only tiny molecules like water can pass through them, and bigger molecules can't.

Both ways

Water constantly trying to even it out.

Doesn't require energy

What is active transport?

Active transport is the movement of particles across a membrane against a concentration gradient from an area of lower concentration to an area of higher concentration using energy transferred during respiration.

Moving up a concentration gradient requires energy unlike the other two.

Essential as allows nutrients to be taken into the blood despite the concentration gradient is the wrong way.

How to investigate osmosis?

-Prepare sucrose solutions of different concentrations ranging from pure water to very concentrated sucrose solution.

-Use a cork borer to cut a potato into the same size pieces, 1cm pieces of potato

-Divide the cylinders into groups of three and use a mass balance to measure the mass of each group.

-Place one group in each solution

-Leave the cylinders in solutions for at least 40 minutes (making sure they all get the same amount)

-Remove the cylinders and pat dry gently with a paper towel. This removes excess water from the surface of the cylinders, so you get more accurate measurements of their final masses.

-Weigh each group again and record your results.

-The only thing that you should change in the experiment is the sucrose solution. Everything else keep the same

How to calculate and interpret your results?

Percentage change= final mass-initial mass/initial mass x100

What are chromosomes?

Coiled up lengths of DNA molecules that contain genetic information

What is a diploid cell?

A cell with two sets of chromosomes, one from mother and one from father.

What does mitosis produce?

two genetically identical daughter cells that have the same number of chromosomes as the parent cell

What are the three uses of mitosis?

growth, repair, asexual reproduction

Interphase

Interphase is 90% of mitosis. The cell has to increase the amount of ribosomes and mitochondria, then it duplicates its DNA- so there is one exact duplicate for each new cell and becomes an X shape.

Prophase

The chromosomes condense, getting shorter and fatter. The membrane around the nucleus breaks and the chromosomes lie free in the cytoplasm.

Metaphase

Chromosomes line up in the middle

Anaphase

Spindle fibres pull chromosomes apart and chromatids are pulled to opposite end of the cell

Telophase

Membrane forms around each set of chromosomes. These become the nuclei of the two cells.

Cytokenesis

The final stage of the cell cycle, in which the cell's cytoplasm divides, distributing the organelles into each of the two new identical diploid daughter cells

How do you calculate the number of cells after mitosis?

Number of cells = 2ⁿ, where n = number of divisions.

Example: 5 divisions → 2⁵ = 32 cells.

What is growth?

increase in size or mass

How do plants and animals grow and develop?

Cell differentiation and cell division.

What is cell differentiation?

when cells become specialised

What is cell division?

by mitosis, the division of a cell into two diploid daughter cells with the same genetic material.

What is the process in which plants grow?

Cell elongation is where a plant cell expands resulting in growth of plant.

How does all growth happen in animals?

Animals grow fast when young but after they grow fully most growth is for repairing of cells, this means that cell differentiation is lost at an early age.

How does growth happen in plants?

Growth in height mainly happens during cell elongation- cell division usually happens in just the tips of roots and shoots in area's called meristems. Plants always are growing and do not lose the capabilities of differentiating cells.

What is cancer?

The rate at which cells divide by mitosis is controlled by the genes in organisms DNA. If a gene mutates, the cell may start dividing uncontrollably forming a tumour. If it invades and destroys other tissue its called a cancer.

What are growth charts used to assess?

- a child's growth over time

- so that an overall pattern in development can be seen and any problems highlighted

What do lines on a percentile graph represent?

They show the differences in and what is average, 50%.

When might doctors be concerned about a child's growth?

If measurements are above/below the extreme percentile lines, shift by two or more percentiles, or show inconsistent patterns (e.g. small body, large head).

What are stem cells?

undifferentiated cells that can differentiate into any type of cell depending on what instructions they're given

Where can stem cells be found?

- embryos- which have the potential to become any cells

- adult bone marrow- are less versatile and usually replace damaged cells like blood or skin.

What are plant stem cells and where are they found?

In meristems (at root and shoot tips), plant stem cells divide and differentiate into any plant cell type resembling the embryonic cell in humans.

How are stem cells used in medicine today?

Adult stem cells can be used to cure some diseases like sickle cell anaemia by bone marrow transplant.

What is the potential of stem cells in future medicine?

Scientists hope to use stem cells to grow specialised cells to replace damaged tissues, e.g. heart muscle cells for heart disease patients.

Name the risks of using stem cells in treatments?

Tumour development, disease transmission, and immune rejection of donor cells

Tumour development

Stem cells divide very quickly. If scientists are unable to control the rate at which the transplanted cells divide inside a patient, a tumour may develop

Disease Transmission

Viruses live inside cells. If donor stem cells are infected with a virus and this isn't picked up by the scientists, the virus could be passed on to the recipient and so make them sicker.

Immune rejection of donor cells

If the transplanted cells aren't grown using the patients own stem cells, the patient's body may recognise the cells as foreign and trigger an immune response to try and kill them. Drugs can be taken to suppress this response but doing this will allow diseases to easily attack the body with a weakened immune system.

What are the ethical concerns about embryonic stem cell research?

Some believe it's wrong to use human embryos as they are potential lives, while others argue curing diseases is more important.

What are neurons?

nerve cells

What do sensory receptors do?

detect stimuli (change in environment) from the external or internal environment and send nerve impulses to the CNS (brain and spinal cords) via sensory neurones.

What is the happens after detecting a stimulus?

Stimulus

Receptor

Sensory Neurone

CNS

Motor Neurone

Effector

Response

How do impulses travel through the CNS?

Along relay neurones

How does the CNS send information?

along a motor neurone and then the effector responds accordingly, the time it takes is called your reaction time.

How are neurones adapted to their function?

All neurones have a cell body with a nucleus (plus cytoplasm and other subcellular structures. The cell body has extensions that connect to other neurones- dendrites and dendrons carry nerve impulses towards the cell body, and axons carry nerve impulses away from the cell body.

What speeds up this process?

Some axons are surrounded by myelin sheath which acts as a electrical insulator, speeding up the electrical impulse. Neurones can be very long, which also speeds up the impulse connecting with another neurone slows the impulse down, so one long neurone is much quicker than lots of short ones joint together.

Sensory neurone

One long dendron carries nerve impulses from receptor cells to the cell body which is located in the middle of the neurone. one short axon carries nerve impulses from the cell body to the CNS

Motor neurone

Many short dendrites carry nerve impulses from the CNS to the cell body. One long axon carries nerve impulses from the cell body to effector cells.

Relay neurone

-Many short dendrites carry nerve impulses from sensory neurones to the cell body

-An axon carries nerve impulses from the cell body to the motor neurones

What is a synapse and how does it work?

A synapse is the gap between 2 nerves - chemicals called neurotransmitters which diffuse across the gap. The neurotransmitters trigger a new electrical signal in the next neurone.

Why is nerve signal transmission slowed at a synapse?

The transmission is generally very fast, but slows down at the synapse.

This happens because the diffusion of neurotransmitters across the gap takes time.

What happens after a stimuli is detected?

When a stimulus affects the pain receptors in the skin. These receptors detect the stimulus and send impulses along a sensory neurone towards the spinal cord.

When the impulses reach a synapse between the sensory neurone and a relay neurone, neurotransmitters are released, which cause the impulses to be passed along the relay neurone.

At the next synapse, between the relay neurone and a motor neurone, the same thing happens — neurotransmitters carry the impulse across.

The impulses then travel along the motor neurone to the effector (in this case, a muscle in the arm).

When the impulses reach the muscle, it contracts and quickly pulls your hand away from the bee — often before you even feel the pain.

This type of response is called a reflex, and it's automatic, rapid, and quicker than normal responses, because it doesn't involve the conscious part of the brain.

How does the human eye protect itself from very bright lights?

Light receptors in the eye detect very bright light and send a message along a sensory neurone to the brain.

The message then travels along a relay neurone to a motor neurone, which tells circular muscles in the iris to contract, making the pupil smaller.

What is sexual reproduction?

Reproduction involving 2 parent organisms combining genetic material to create a genetically different offspring.

What is a gamete?

is a haploid sex cell, sperm and egg cell which are capable of sexual reproduction to form a zygote which ends up with the full set of chromosomes so it is diploid.

How does the zygote develop from that point?

by mitosis and develops into an embryo. This embryo has characteristics from both mother and father.

How are gametes produced?

by meiosis

What is meiosis?

Meiosis is a type of cell division that produces gametes

produces haploid cells

which only occurs in ovaries and testes

genetically different

diploid cell

What happens during the first division of meiosis?

duplicates its DNA so there's enough for each new cell

there will be 2 cells after this first division

chromosomes line up in pairs in the middle of cells

one chromosome from mother and another from father

then the pairs are pulled apart so each new cell only has one copy of chromosomes.

each of the new cells will have a mix of mother and father causing genetic variation