Edexcel GCSE Biology

In which type of cell would you find a cell wall, chloroplasts and a vacuole?

plant cell

What does an animal cell have?

- cytoplasm

- nucleus

- ribosomes

- cell membrane

- mitochondria

What does the nucleus do?

contains genetic material that controls the activities of the cell

What is the cytoplasm?

gel-like substance where most of the chemical reactions happen. It contains enzymes which control these chemical reactions

What is the cell membrane

holds the cell together and controls what goes in and out

What happens in the mitochondria?

these are where most of the reactions for respiration take place. Respiration releases energy that the cell needs to work

What happens in the ribosomes?

these are where proteins are made in the cell

What does a bacterial cell NOT have?

a nucleus- genetic material floats in the cytoplasm

What is a yeast cell an example of?

a single cell organism

What does a yeast cell have?

- nucleus

- cytoplasm

- cell membrane

- surrounding cell wall

How is a leaf cell different from a yeast cell?

leaf cells have chloroplasts and a cellulose cell wall. yeast cells have neither

What is the definition of diffusion?

the SPREADING OUT of PARTICLES from an area of HIGH CONCENTRATION to an area of LOW CONCENTRATION

or

the NET MOVEMENT of PARTICLES down a CONCENTRATION GRADIENT

What substances can diffuse through cell membranes?

small molecules like oxygen, glucose, amino acids and water

What substances can't diffuse through cell membranes?

big molecules like starch and proteins

What are some examples of diffusion?

- the diffusion of oxygen into the cells of the body from the bloodstream as the cells are respiring (and using up oxygen)

- the diffusion of carbon dioxide into actively photosynthesising plant cells

- the diffusion of simple sugars and amino acids for the gut through cell membranes

When, and in which direction, will diffusion take place in solutions and in gases?

- if two solutions are separated by a cell membrane, particles will move from a region of high concentration to a region of low concentration

- gases will also diffuse through the air from a region of high concentration to a region of low concentration

How is a leaf cell adapted to carry out photosynthesis?

- the leaf has mesophyll tissue

- the mesophyll cells contain chloroplasts which can photosynthesise

How are palisade cells adapted for photosynthesis?

- packed will chloroplasts for photosynthesis

- tall shape means a lot of surface area exposed down the side for absorbing carbon dioxide from the air in the leaf

- they are grouped together at the top of the leaf so that they can absorb more sunlight

How are red blood cells adapted to carry oxygen?

- concave shape gives a big surface area for absorbing oxygen. it also helps them pass smoothly through capillaries to reach body cells

- packed with haemoglobin which absorbs oxygen

- they have no nucleus to leave even more room for haemoglobin

How are sperm cells adapted for swimming to the egg?

- streamlined head and flagella to help it swim to the egg

- there are a lot of mitochondria in the cell to provide the energy needed

- carry enzymes in their heads to digest through the egg cell membrane

If a cell has many mitochondria...

it must need a lot of energy, e.g. muscle cell, sperm cell

If a cell has many ribosomes...

it is making a lot of protein, e.g. gland cells which produce enzymes

If a cell has flagella..

it must be able to move, e.g. sperm cells

What is the process by which cells become specialised?

differentiation

What is meant by the term differentiation of cells?

- when cells start to divide they are very similar

- as the tissues develop the cells change to form particular function

What is a tissue?

a group of similar cells that work together to carry out a particular function

What sort of tissue can you find in mammals?

- Epithelial tissue: covers some parts of the body, e.g. the inside and outside of the gut

- Muscular tissue: contracts to move whatever its attached to

- Glandular tissue: makes and secretes chemicals like hormones and enzymes

What is an organ?

a group of different tissues that work together to perform a certain function, e.g. stomach

What tissues are the stomach made up of and what are their purposes?

- Epithelial tissue: covers the inside and outside of the stomach

- Muscular tissue: contracts the stomach wall to churn up the food

- Glandular tissue: produces digestive juices to digest food

What is an organ system?

a group of organs working together to perform a particular function, e.g. the digestive system breaks down food

What organs does the digestive system include?

- glands

- the stomach

- the liver

- the small intestine

-the large intestine

What two glands produce digestive juices?

pancreas and salivary glands

what does both the stomach and small intestine do?

digest food

What does the liver do?

produces bile

What does the small intestine do?

absorbs soluble food molecules

What does the large intestine do?

absorbs water from undigested food leaving faeces

Describe in detail what happens to food as it passes through the digestive system?

- the insoluble food is mixed with digestive juices produces by glands

- it is digested in the stomach and small intestine

- bile produced by the liver is added to the food to help digestion

- absorption of the soluble food takes place in the small intestine

- water is absorbed by the large intestine

What are the plant organs?

stems, leaves and roots

What are the tissues found in plants?

-Mesophyll tissue- where most of the photosynthesis occurs in the plant

- Xylem and Phloem- transport things like water, mineral ions and sucrose around the plant

- Epidermal tissue- this covers the whole plant

What is photosynthesis?

the process that produces 'food' in plants and algae. the 'food' it produces is glucose

Name the solution used to test a leaf for starch?

iodine solution

What is the result of iodine test for start

- the regions containing starch will turn blue-black

- the regions without starch will turn yellow-brown

What does the test for starch show us?

if photosynethsis has occurred

Where does photosynthesis happen?

inside the chloroplasts

What is chlorophyll?

a green substance found in chloroplasts which absorbs sunlight and uses it to convert carbon dioxide (from the air) and water (from the soil) into glucose. oxygen is a by-product

What are the top, middle and bottom layers of a leaf?

top - upper epidermis

middle - spongy mesophyll

bottom - lower epidermis

Where is chlorophyll found?

in the chloroplasts

How is water transported in the plant?

through the xylem

How are sugars transported in plants?

through the phloem

What is the equation for photosynthesis?

Carbon dioxide + Water ---(sunlight)---> Glucose + Oxygen

What is a limiting factor?

something that is stopping photosynthesis happening faster

What are the three limiting factors in photosynthesis?

- light

- temperature

- carbon dioxide

Why do limiting factor graphs 'level off' after a certain point?

because the rate of photosynthesis can only be raised up to a certain point, until something else becomes a limiting factor

At what temperature do the enzymes for photosynthesis become denatured?

45 degrees Celsius

How is light controlled in a green house?

light is always needed for photosynthesis so artificial light can be provided once the sun goes down to give plants more photosynthesis time

How is temperature controlled in a green house?

- greenhouses help trap the suns heat and make sure that the temperature doesn't become limiting.

- heater may be used during the winter to keep the temperature at the ideal level

- shades and ventilation if it's too hot to cool things down

How are carbon dioxide levels controlled in a green house?

increase carbon dioxide levels by using a paraffin heater. as the paraffin burns it makes CO2 as a by-product

How are plants protected from pests and diseases?

- kept enclosed in a greenhouse

- add fertilizers to the soil as well, to provide minerals for healthy growth

What is the independent variable?

the one being tested, e.g. concentration of carbon dioxide (x axis)

What is the dependent variable?

the one you measure, e.g. usually the volume of oxygen produced (y axis)

What are the four ways in which plants use glucose?

- for respiration

- making cell walls

- making proteins

- storage as lipids in seeds

- storage as starch

Name three substances used for storage in plants?

starch, fats and oil

How is glucose made from photosynthesis used to make cell walls?

glucose converted to cellulose for making strong cell walls, especially in a rapidly growing plant

How is glucose made from photosynthesis used to make proteins?

glucose is combined with nitrate ions (absorbed from soil) to make amino acids, which are then made into proteins

How is glucose made from photosynthesis stored in seeds?

glucose is turned into lipids (fats & oils) for storing in seeds, e.g. sunflower seeds contain a lot of oil (we get cooking oil and margarine)

Where is glucose made from photosynthesis stored as starch?

Glucose is turned into starch and stored in the roots, stems and leaves for when photosynthesis isn't happening e.g. winter.

Why is starch good for storing in plants?

starch is insoluble which makes it much better for storing than glucose - a cell with lots of glucose in would draw in loads of water and swell up

What is a habitat?

the place where an organism lives, e.g. a playing field

What is the distribution of an organism?

where an organism is found, e.g. in a part of the playing field

What five things affect the distribution of organisms?

- temperature

- amount of light

- availability of:

- water

- nutrients

- oxygen & carbon dioxide

What are two ways that you can study the distribution of small organisms?

- by using quadrats we can measure how common an organism is in two sample areas and compare them

- by placing quadrats along a transect we can study how the distribution changes across and area

What is a quadrat?

a square frame enclosing a known area

How to use a quadrat.

1. place a quadrat on the ground at a random point within the first sample area

2. count all the organisms within the quadrat

3. repeat steps 1 and 2 as many times as you can

4. work out the mean number of organisms per quadrat with in the first sample area (TOTAL number of organisms ÷ NUMBER of quadrats)

5. repeat steps 1-4 in the second area

6. compare two means

How do you work out the population size?

mean number of organisms per m² x total area (in m²) of the habitat

What is a transect?

lines used to help find out how organisms (like plants) are distributed across an area, e.g. if an organisms becomes more or less common as you move from a hedge towards the middle of a field

How to use a transect with a tape measure.

1. mark out a line in the area you want to study using a tape measure

2. then collect data along the line

3. you can do this by just counting all the organisms you're interested in that touch the line

What is the range?

the difference between the minimum and maximum reading

How to use a transect with a quadrat.

quadrats can be placed next to each other along the line or at intervals, e.g. every 2m

What is the mean?

the sum of the readings divided by the number of readings taken

What is the median?

the middle value of the readings when written in order

What is the mode?

the reading that appears most frequently

How can you make your results more reliable (valid, reproducible, repeatable)?

take a large sample size e.g. use as many quadrats and transects as possible in your sample area. bigger samples are more representative of the whole population so its more reliable

How can you make your results valid

- control variables, e.g. do it at the same time of day

- use random samples e.g. randomly put down or mark out your quadrat or transect. if all your samples are in one spot, and everywhere else is different, the results wont be valid

How can you make your results repeatable?

- if the original experimenter repeats the investigation using the same method and equipment and obtains the same results

- however sometimes the experimenter may be making the same mistake every time and get repeatable results

- so it may also be necessary to check the results to ensure that they are reproducible

What is meant by 'reproducible'?

if the investigation is repeated by another person or by using different equipment or techniques, and the same results are obtained

What do enzymes act as?

biological catalysts- they speed-up reactions

What is a catalyst?

a substance that INCREASES the speed of a reaction without being CHANGED or USED UP in the reaction

What are enzymes made up of?

proteins, which are made up of chains of amino acids

Why are enzymes picky?

- the shape of an enzyme is vital for its function

- this shape has an area where other molecules can fit (the active site)

- the substrate in a reaction can be held in the active site and either be connected to another molecule or broken down

Enzymes can...

- build large molecules from many smaller ones, e.g. building starch from glucose molecules

- change one molecule into another one, e.g. convert one type of sugar into another one

- break down large molecules into smaller ones, e.g. all the digestive enzymes to this

What happens when the temperature is too high?

- at first the higher temperature increases the rate of reaction

- but if it gets too hot, the bonds holding the enzyme together will break

- this destroys the enzymes special shape, and so it wont work anymore

What temperature do enzymes in the human body usually work best at?

37 degrees Celsius

What happens to enzymes if the pH is too high or too low?

It interferes with the bonds holding the enzyme together - changing its's shape and denaturing it

Whats the most common optimum pH

its often pH 7- neutral but not always

Whats the optimum pH of enzymes in the stomach?

pH 2- well-suited to acidic conditions

What do digestive enzymes do?

break down big molecules into smaller ones

What are examples of big molecules (in digestion)?

starch, proteins and fats

- they're too big to pass through the walls of the digestive system

What are examples of smaller molecules (in digestion)?

sugars, amino acids, glycerol and fatty acids

- they can pass easily through the walls of the digestive system

What does amylase do?

converts starch to sugars in the mouth and small intestine

What does protease do?

converts proteins to amino acids in the stomach and small intestine