AQA GCSE Biology - Paper 1

What does a vacuole do?

What does a vacuole do?

It contains cell sap and helps maintain the shape of the cell

What does a nucleus do?

It contains genetic material and controls the activities of the cell

What does cytoplasm do?

It's a gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions

What does a cell membrane do?

It holds the cell together and controls what goes in and out

What do mitochondria do?

These are where most of the reactions for aerobic respiration occur. Respiration transfers energy that the cell needs to work

What do ribosomes do?

This is where protein synthesis takes place - where proteins are made in the cell

What do cell walls do?

They are made of cellulose and they support and strengthen the cell

What do chloroplasts do?

This is where photosynthesis occurs, which makes food for the plant. They contain chlorophyll - a green pigment - which absorbs light needed for photosynthesis

What do bacterial cells contain?

Cytoplasm, cell membrane, cell wall, flagella, ribosomes, mitochondria, slime capsule, plasmids (small rings of DNA) and a single circular strand of DNA that floats freely in the cytoplasm

What do bacterial cells NOT contain?

A nucleus

What is the equation for magnification?

Image size divided by actual size

What is differentiation?

The process by which a cell changes to become specialised for its job

What are undifferentiated cells called?

Stem cells

What are sperm cells specialised for and how are they specialised?

Reproduction - they transport the male DNA to the female DNA

-It has a flagella and a streamlined head to help it swim towards the egg

-There are lots of mitochondria in the cell to provide the energy needed

-It carries enzymes in its head to help digest through the egg cell membranes

What are nerve cells specialised for and how are they specialised?

Rapid signalling - they carry electrical signals from one part of the body to another

-They are long to cover more distance

-They have branched connections at their ends to connect to other nerve cells and form a network throughout the body

What are muscle cells specialised for and how are they specialised?

Contraction - they need to contract quickly

-They are long so they have space to contract

-They contain lots of mitochondria to generate the energy needed for contraction

What are root hair cells specialised for and how are they specialised?

Absorbing water and minerals

-They are cells on the surface of plant roots which grow into long hairs that stick out into the soil

-They have a large surface area for absorbing water and mineral ions from the soil

What are chromosomes?

Coiled up lengths of DNA molecules that are found in the nuclei

What do multicellular organisms use mitosis for?

To grow or replace cells that have been damaged

What are stem cells?

They are undifferentiated cells that divide to produce lots more undifferentiated cells. They then differentiate into different types of cell

Where are stem cells found?

In early human embryos or the bone marrow of adults

What do embryonic stem cells do?

1) Used to replace faulty cells in sick people - insulin-producing cells for diabetes and nerve cells for paralysed spinal injuries

2) Used to replace faulty blood cells

What is diffusion?

Diffusion is the movement of particles from an area of high concentration to an area of low concentration

Name the substances that can diffuse through cell membranes

Glucose, water, oxygen and amino acids

Name two substances that can't diffuse through cell membranes

Protein and starch

What is osmosis?

Osmosis is the passive movement of water molecules through a partially permeable cell membrane from an area of high water concentration to an area of low water concentration

What are the two main differences between active transport and diffusion?

Active transport uses energy whereas diffusion doesn't. Active transport goes against the concentration gradient whereas diffusion goes along it

Adaptations of Exchange Surfaces

1) Large surface area - lots of substances can diffuse at once

2) Lots of blood vessels - to get stuff into and out of the blood quickly

3) Thin membrane - short distance for substances to diffuse

4) Often ventilated - air moves in & out

Give two ways that the villi in the small intestine are adapted for absorbing digested food

1) A single layer of surface cells

2) A very good blood supply to assist quick absorption

Explain how the leaves are adapted to maximise the amount of carbon dioxide that gets into their cells

1) The exchange surface in a leaf is covered in stomata which the carbon dioxide diffuses through

2) The leaf has a flattened shape which increases the area of its exchange surface, therefore it's more effective

3) The walls of the cells inside the leaf act as another exchange surface

4) The air spaces inside the leaf increase the area of the exchange surface which increases the chance for carbon dioxide to enter the cells

What affects the rate of diffusion?

Concentration gradient - the steeper the gradient, the faster the rate

Temperature - the higher the temperature, the faster the rate (the particles have more energy thus move around faster)

Surface area - the larger it is, the faster the rate

Diffusion distance - the shorter the distance, the faster the rate

Examples of active transport

Plants = Root hairs absorb minerals and water. Each branch of a root will be covered in tiny hairs, therefore increasing the surface area for the absorption of minerals and water. The concentration of minerals is usually higher in the root hair cells than in the soil around them, therefore they can't use diffusion for this process.

Animals = Glucose is taken in from the gut and from kidney tubules.

How are alveoli in the lungs specialised to maximise the diffusion of oxygen and carbon dioxide?

-an enormous surface area

-a moist lining for dissolving gases

-very thin walls

-a good blood supply

How do fish respire?

-Water enters the fish through the mouth and passes out through the gills

-During this process, oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water

How are fish adapted for gas exchange?

-Each gill is made up of lots of gill filaments which create a large surface area for the exchange of gases

-Gill filaments are covered in lamellae which increase the surface even more

-The lamellae have lots of blood capillaries to speed up diffusion

-The lamellae have a thin surface layer of cells to minimise the diffusion distance

-Blood flows through the lamellae one way and water flows over in the opposite direction which maintains a higher concentration gradient between the blood and the water

-The concentration of oxygen in the water is always higher than that in the blood to maximise the amount of oxygen diffusion from the water into the blood

Microscopy Practical - Preparing the Slide

1) Add a drop of water to the middle of a clean slide

2) Cut up an onion & separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers

3) Using the tweezers, place the epidermal tissue into the water on the slide

4) Add a drop of iodine solution - a stain used to highlight objects in a cell by adding colour to them

5) Place a cover slip on top - stand the cover slip upright on the slide, next to the water droplet. Then, carefully tilt & lower it so it covers the specimen. Try not to get any air bubbles under there - there'll obstruct your view

Microscopy Practical - Using a Light Microscope

1) Clip the slide you've prepared onto the stage

2) Select the lowest-powered objective lens

3) Use the coarse adjustment knob to move the stage up to just below the objective lens

4) Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus

5) Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide

Microscopy Practical - Drawing Observations

1) Draw what you see under the microscope using a pencil with a sharp point

2) Make sure your drawing takes up at least half of the space available & that it is drawn with clear, unbroken lines

3) Your drawing should not include any colouring or shading

4) If you are drawing cells, the subcellular structures should be drawn in proportion

5) Include a title & write down the magnification that it was observed under

6) Label the important features of your drawing using straight, uncrossed lines

What happens during binary fission?

1) The circular DNA & plasmid(s) replicate

2) The cell gets bigger & the circular DNA strands move to opposite poles of the cell

3) The cytoplasm begins to divide & new cell walls begin to form

4) The cytoplasm divides & two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s)

What is binary fission?

A type of simple cell division used by prokaryotic cells to reproduce & split into two

What conditions do bacteria need to divide?

1) Warm environment

2) Lots of nutrients

What is the mean division time?

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

How do you make an agar plate?

Hot agar jelly is poured into shallow Petri dishes. When the jelly's cooled & set, inoculating loops can be used to transfer the microorganisms to the culture medium. Alternatively, a sterile dropping pipette & spreader can be used to get an even covering of bacteria. The microorganisms then multiply

Investigating the Effect of Antibiotics on Bacterial Growth - Method

1) Place paper discs soaked in different types 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 that aren't affected by the antibiotic 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 - an inhibition zone

3) Make sure you use a control - a paper disc that has not been soaked in an antibiotic. Instead, soak it in sterile water so you can be sure that any difference between the growth of bacteria around the control disc & around one of the antibiotic discs is due to the effect of the antibiotic alone

4) Leave the plate for 48 hours at 25°C

5) The more effective the antibiotic is, the large the inhibition zone will be

Avoiding Contamination

1) The Petri dishes & culture medium must be sterilised before use (heating to a high temperature), to kill any unwanted microorganisms

2) If an inoculating loop is used to transfer the bacteria to the culture medium, it should be sterilised first by passing it through a hot flame

3) After transferring the bacteria, the lid of the Petri dish should be lightly taped on - stops any microorganisms from the air getting it

4) The Petri dish should be stored upside down - stops drops of condensation falling onto the agar surface

Investigating the Effect of Sugar Solutions on Plant Tissue - Method

1) Cut up a potato into identical cylinders, and get some beakers with different sugar solutions in them: one should be pure water & another should be a very concentrated sugar solution

2) Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours

3) Take them out, dry them with a paper towel & measure their masses again

4) If the cylinders have drawn in water by osmosis, they'll have increased in mass. If water has been drawn out, they'll have decreased in mass

5) The dependent variable is the chip mass & the independent variable is the concentration of the sugar solution. All other variables must be kept the same

Possible Errors of the Potato Chip Experiment

1) Some potato cylinders were not fully dried

2) Water evaporated from the beakers

3) The potato chips weren't identical sizes

4) The volumes of water weren't identical

Types of eukaryotic cells

Animal cells

Plant cells

What are light microscopes?

They use light & lenses to form an image of a specimen & magnify it

Allow us to see individual cells & large subcellular structures e.g. nuclei

What are electron microscopes?

They use electrons to form an image

They have a higher magnification & a higher resolution

Allow us to see smaller things in more detail e.g. internal structure of mitochondria & chloroplasts & ribosomes & plasmids

Disadvantages of Stem Cells

1) Stem cells grown in the lab may become contaminated with a virus - this will be passed onto the patient & make them sicker

2) Some people think that human embryos shouldn't be used for experiments - each one is a potential human life

3) Scientists should focus more on finding & developing other sources of stem cells

What is a tissue?

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

Examples of tissues

Muscular tissue - contracts to move whatever it's attached to

Glandular tissue - makes and secretes chemicals like enzymes and hormones

Epithelial tissue - covers some parts of the human body e.g. the inside of the gut

What is an organ system?

An organ system is a group of organs working together to carry out a particular function

Example of an organ system

Digestive system - glands (pancreas and salivary glands), stomach, liver, small intestine and large intestine

Why can enzymes be described as biological catalysts?

They speed up useful chemical reactions in the body

Why do enzymes only usually catalyse one reaction?

Their active site is only complimentary to one type of substrate

What does it mean when an enzyme is denatured?

Its active site has changed shape due to intense heat or acidic conditions

Where is amylase found?

It's made in the salivary gland and the pancreas and it works in the small intestine

What is the role of lipases?

They break down lipids into fatty acids and glycerol

Where is bile made and stored?

It's made in the liver and stored in the gall bladder

What does bile do?

It emulsifies fats into smaller, more soluble pieces which gives the fat a bigger surface area for lipase to work on. It also neutralises the stomach acid to make the conditions alkaline, therefore the enzymes can work in the small intestine

What are organs?

Organs are groups of tissues that work together to perform certain functions

What are the tissues in the stomach and what do they do?

Muscular tissue - moves the stomach wall to churn up the food

Glandular tissue - makes digestive juices to digest food

Epithelial tissue - covers the inside and outside of the stomach

What is the name of the substance when a substrate fits into the enzyme's active site?

Enzyme substrate complex

What is the name of the substance when the enzyme's active site has turned the substrate into two products?

Enzyme product complex

What is the optimum pH for enzymes?

The pH level that they are most active at. E.g., pepsin has an optimum pH of 2

What does amylase break down?

It catalyses the breakdown of starch to maltose

What do carbohydrases break down?

Carbohydrates into simple sugars

What do proteases break down?

Proteins into amino acids

Where are proteases found?

They're made in the stomach (called pepsin here) and the pancreas and found in the small intestine

Where are lipases found?

They're made in the pancreas and work in the small intestine

Name three substances and what they test for

Benedict's Test - testing for sugars - goes red

Iodine solution - tests for starch - goes blue-black

Biuret Test - tests for proteins - goes purple

What do the salivary glands do?

They produce amylase in the saliva

What does the stomach do?

-It pummels the food with its muscular walls

-It produces pepsin

-It produces hydrochloric acid to kill bacteria and give the right pH for pepsin to work

What does the pancreas do?

It produces amylase, protease and lipase then releases them into the small intestine

What does the small intestine do?

It contains protease, amylase and lipase to complete digestion. Digested food is absorbed into the blood here

What does the rectum do?

It stores faeces

What does the large intestine do?

It's where excess water is absorbed from the food

What does the gall bladder do?

It stores bile before it's released into the small intestine

What does the liver do?

It produces bile which neutralises stomach acid and emulsifies fat

Where are the lungs?

The thorax

What are the lungs surrounded by?

Pleural membrane

What protects the lungs?

The ribcage

What goes down the trachea?

The air that you breathe in

What tubes join onto the trachea?

The bronchi

What do the bronchi split off into?

Bronchioles

What are the small bags at the end of bronchioles called?

Alveoli

What happens in an alveolus?

Gas exchange. The blood passing next to the alveoli contains lots of carbon dioxide and little oxygen. The oxygen diffuses out of the alveoli (high concentration) and into the blood (low concentration) and the carbon dioxide diffuses out of the blood (high concentration) and into the alveoli (low concentration) to be breathed out.

What surrounds the alveoli?

Lots of blood capillaries

What happens when blood reaches body cells?

Oxygen is released from the red blood cells and diffuses into the body cells. At the same time, carbon dioxide diffuses out of the body cells and into the blood. It's then carried back to the heart

What makes up the circulatory system?

The heart, blood vessels and blood

What happens on the right side of the heart?

Deoxygenated blood flows in through the vena cava and into the right atrium. The atrium contracts and pushes the blood through the tricuspid valve, into the right ventricle. The valve closes and the ventricle contracts, to push the blood through the right semi-lunar valve. The valve will close and the blood is pushed out of the pulmonary artery to go up to the lungs

What happens on the left side of the heart?

Oxygenated blood flows in through the pulmonary vein and into the left atrium. The atrium contracts and pushes the blood through the bicuspid valve, into the left ventricle. The valve closes and the ventricle contracts to push the blood through the left semi-lunar valve. The valve will then close and the blood flows out of the aorta to all the cells in the body for gas exchange

How does the heart pump blood around the body?

Blood flows into the two atria from the vena cava (right atrium) and the pulmonary vein (left atrium). The atria contract, pushing the blood into the ventricles through valves. The ventricles contract and force the blood through more valves into the pulmonary artery (right ventricle) and the aorta (left ventricle) and out of the heart

What are the three types of blood vessels?

Arteries, capillaries and veins

What do arteries do?

-They carry blood under high amounts of pressure

-Their walls are strong, elastic and thick

-They have the smallest lumens

-They contain thick layers of muscle to make them strong and elastic fibres to allow them to stretch and spring back

What do capillaries do?

-Arteries branch into capillaries

-They are really tiny - too small to see

-They carry blood really close to every cell in the body to exchange substances with them

-They have permeable walls - substances can diffuse in and out

-They supply food and oxygen and take away waste like carbon dioxide

-Their walls are one cell thick - this increases the rate of diffusion

What do veins do?

-Capillaries join up to form veins

-The blood is at low pressure in the veins so the walls aren't as thick as an artery's

-They have the biggest lumen to help the blood flow despite the lower pressure

-They have valves to help keep the blood flowing in the right direction

What is the rate of blood flow?

Volume of blood divided by the number of minutes