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AQA GCSE Biology - Paper 1
What does a nucleus do? - correct answer It contains genetic material and controls the activities of the cell What does cytoplasm do? - correct answer 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? - correct answer It holds the cell together and controls what goes in and out What do mitochondria do? - correct answer These are where most of the reactions for aerobic respiration occur. Respiration transfers energy that the cell needs to work What do ribosomes do? - correct answer This is where protein synthesis takes place - where proteins are made in the cell What do cell walls do? - correct answer They are made of cellulose and they support and strengthen the cell What does a vacuole do? - correct answer It contains cell sap and helps maintain the shape of the cell What do chloroplasts do? - correct answer 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? - correct answer 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? - correct answer A nucleus
What is the equation for magnification? - correct answer Image size divided by actual size What is differentiation? - correct answer The process by which a cell changes to become specialised for its job What are undifferentiated cells called? - correct answer Stem cells What are sperm cells specialised for and how are they specialised? - correct answer 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? - correct answer 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? - correct answer 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? - correct answer 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? - correct answer Coiled up lengths of DNA molecules that are found in the nuclei
- Thin membrane - short distance for substances to diffuse
- Often ventilated - air moves in & out Give two ways that the villi in the small intestine are adapted for absorbing digested food - correct answer 1) A single layer of surface cells
- 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 - correct answer 1) The exchange surface in a leaf is covered in stomata which the carbon dioxide diffuses through
- The leaf has a flattened shape which increases the area of its exchange surface, therefore it's more effective
- The walls of the cells inside the leaf act as another exchange surface
- 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? - correct answer 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 - correct answer 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? - correct answer -an enormous surface area -a moist lining for dissolving gases -very thin walls
-a good blood supply How do fish respire? - correct answer -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? - correct answer -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 - correct answer 1) Add a drop of water to the middle of a clean slide
- 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
- Using the tweezers, place the epidermal tissue into the water on the slide
- Add a drop of iodine solution - a stain used to highlight objects in a cell by adding colour to them
- 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 - correct answer 1) Clip the slide you've prepared onto the stage
- Select the lowest-powered objective lens
- Use the coarse adjustment knob to move the stage up to just below the objective lens
- Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus
Investigating the Effect of Antibiotics on Bacterial Growth - Method - correct answer 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
- 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
- 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
- Leave the plate for 48 hours at 25°C
- The more effective the antibiotic is, the large the inhibition zone will be Avoiding Contamination - correct answer 1) The Petri dishes & culture medium must be sterilised before use (heating to a high temperature), to kill any unwanted microorganisms
- 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
- After transferring the bacteria, the lid of the Petri dish should be lightly taped on - stops any microorganisms from the air getting it
- 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 - correct answer 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
- Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours
- Take them out, dry them with a paper towel & measure their masses again
- 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
- 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 - correct answer 1) Some potato cylinders were not fully dried
- Water evaporated from the beakers
- The potato chips weren't identical sizes
- The volumes of water weren't identical Types of eukaryotic cells - correct answer Animal cells Plant cells What are light microscopes? - correct answer 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? - correct answer 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 - correct answer 1) Stem cells grown in the lab may become contaminated with a virus - this will be passed onto the patient & make them sicker
- Some people think that human embryos shouldn't be used for experiments - each one is a potential human life
- Scientists should focus more on finding & developing other sources of stem cells What is a tissue? - correct answer A tissue is a group of similar cells that work together to carry out a particular function Examples of tissues - correct answer 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? - correct answer An organ system is a group of organs working together to carry out a particular function
What is the name of the substance when a substrate fits into the enzyme's active site? - correct answer Enzyme substrate complex What is the name of the substance when the enzyme's active site has turned the substrate into two products? - correct answer Enzyme product complex What is the optimum pH for enzymes? - correct answer The pH level that they are most active at. E.g., pepsin has an optimum pH of 2 What does amylase break down? - correct answer It catalyses the breakdown of starch to maltose What do carbohydrases break down? - correct answer Carbohydrates into simple sugars What do proteases break down? - correct answer Proteins into amino acids Where are proteases found? - correct answer They're made in the stomach (called pepsin here) and the pancreas and found in the small intestine Where are lipases found? - correct answer They're made in the pancreas and work in the small intestine Name three substances and what they test for - correct answer 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? - correct answer They produce amylase in the saliva What does the stomach do? - correct answer -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? - correct answer It produces amylase, protease and lipase then releases them into the small intestine What does the small intestine do? - correct answer It contains protease, amylase and lipase to complete digestion. Digested food is absorbed into the blood here What does the rectum do? - correct answer It stores faeces What does the large intestine do? - correct answer It's where excess water is absorbed from the food What does the gall bladder do? - correct answer It stores bile before it's released into the small intestine What does the liver do? - correct answer It produces bile which neutralises stomach acid and emulsifies fat Where are the lungs? - correct answer The thorax What are the lungs surrounded by? - correct answer Pleural membrane What protects the lungs? - correct answer The ribcage What goes down the trachea? - correct answer The air that you breathe in What tubes join onto the trachea? - correct answer The bronchi What do the bronchi split off into? - correct answer Bronchioles What are the small bags at the end of bronchioles called? - correct answer Alveoli
-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? - correct answer -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? - correct answer -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? - correct answer Volume of blood divided by the number of minutes What are the four components of blood? - correct answer Red blood cells, white blood cells, platelets and plasma What do red blood cells do? - correct answer -They carry oxygen from the lungs to all the cells in the body -They have a biconcave disc shape - creates a large surface area and allows them to fit through capillaries -They have no nucleus - can store even more oxygen -They contain haemoglobin - this binds to oxygen to form oxyhaemoglobin
What do white blood cells do? - correct answer -They can change shape to ingest microbes - this process is phagocytosis -Others produce antibodies to fight microbes -Some produce antitoxins to neutralise any toxins produced by the microbes -They have a nucleus What do platelets do? - correct answer -They are small fragments of cells that have no nucleus -They help the blood to clot at a wound - stops blood pouring out and microbes getting into your bloodstream -Lack of platelets can cause excessive bleeding and bruising What does plasma do? - correct answer Plasma carries: -red blood cells -white blood cells -glucose -amino acids -carbon dioxide -urea -hormones -proteins -antibodies -antitoxins What are stents? - correct answer -Tubes that are inserted inside arteries to keep them open which allows the blood to pass through to the heart muscles -They lower the risk of a heart attack in people with coronary heart disease -They are effective for a long time -There is a risk of infection from surgery and the patient could develop a blood clot near the stent - thrombosis
What is artificial blood used for? - correct answer -It's a blood substitute (e.g. a salt solution) which can replace a large lost volume of blood -It's safe and can generally keep people alive no matter how big the blood loss -It gives the patient time to develop new blood cells or time to wait for a blood transfusion What is health? - correct answer The state of physical and mental wellbeing What are communicable diseases? - correct answer Diseases that can be spread from person to person or between animals and people. They can be caused by pathogens and can be described as contagious or infectious. Examples include measles and malaria What are non-communicable diseases? - correct answer Diseases that cannot be spread between people or between animals and people. They generally last for a long time and get worse slowly. Example include asthma, cancer and coronary heart disease What's the problem with a weak immune system? - correct answer You have an increased chance of suffering from communicable diseases (e.g. the flu) because the body is less likely to be able to defend itself against the pathogen that causes the disease What can some types of cancer be triggered by? - correct answer Infection by certain viruses E.g. the hepatitis virus can cause long-term infections in the liver which increases the chance of getting liver cancer. Also, infection with HPV can cause cervical cancer What are asthma sufferers in danger of? - correct answer Their symptoms becoming worse - immune system reactions in the body caused by infection by a pathogen can trigger allergic reactions (e.g. skin rashes) or worsen the symptoms of asthma How can be mental health problems be triggered? - correct answer When someone is suffering from severe physical body problems, especially if they have an impact on their ability to do normal activities or affect their life expectancy What factors can affect you health? - correct answer 1) Balanced diet - provides your body with everything it needs
- Stress - being constantly under lots of stress can lead to health issues
- Life situation - having easy access to medicine or things that can prevent illness e.g. buy healthy food or condoms to prevent catching an STD What are risk factors? - correct answer Things that are linked to an increase in your chance of contracting a disease E.g. smoking, obesity, drinking, exposure to radiation Smoking as a risk factor - correct answer Causes cardiovascular disease, lung disease and lung cancer. It damages the walls of arteries and the cells in the lining of the lungs Obesity as a risk factor - correct answer Causes Type 2 diabetes - makes the body less sensitive to insulin Drinking as a risk factor - correct answer Drinking too much alcohol causes liver disease, affects brain function and damages the nerve cells in the brain Exposure to radiation as a risk factor - correct answer Cancer can be caused by exposure to ionising radiation, a carcinogen (something that causes cancer) What are benign tumours? - correct answer Tumour grows until there's no more room The tumour stays in once place (usually in a membrane) Isn't dangerous or cancerous What are malignant tumours? - correct answer Tumours grow and spread to nearby healthy tissues - invading these tissues forms secondary tumours Cells can break off and spread to other parts of the body via the bloodstream Is dangerous and cancerous - can be fatal Risk factors for cancer - correct answer Smoking - lung, mouth, bowel, stomach and cervical cancer Obesity - bowel, liver and kidney cancer
Transport food substances in both directions - translocation Xylem - correct answer Made up of dead cells Transports water and mineral ions from the roots to the stem and the leaves Transports them one way only Movement of water from the roots, through the xylem and out of the leaves is called transpiration What is transpiration? - correct answer The loss of water from plants by evaporation Water evaporates from the leaves Side effect of photosynthesis How does light intensity affect transpiration? - correct answer The brighter the light, the greater the rate In bright light, the stomata will stay open for longer How does temperature affect transpiration? - correct answer The warmer it is, the faster the rate The hotter it gets, the more kinetic energy the water molecules gain How does air flow affect transpiration? - correct answer The better the air flow around a leaf, the greater the rate A good air flow will sweep water vapour away which maintains a low concentration gradient of water in the air outside the leaf Diffusion happens quicker from an area of high concentration to an area of low concentration How does humidity affect transpiration? - correct answer The drier the air around a leaf, the faster the rate Humid air contains lots of water, so the lower the humidity, the faster diffusion will take place How are guard cells adapted to open and close stomata? - correct answer When the plant has lots of water, they fill with water and become turgid - opens the stomata When the plant is short of water, they lose water and become flaccid - closes the stomata
Thin outer walls and thicker inner walls control the opening and closing Sensitive to light so they close at night What is a pacemaker? - correct answer A group of cells in the right atrium wall that control the resting heart rate They produce a small electrical impulse which spreads to the surrounding muscle cells, causing them to contract Artificial pacemakers can be used to control heartbeat if the natural pacemaker cells don't work well e.g. irregular heartbeat - they are little devices implanted under the skin and have a wire going to the heart - they produce an electric current to keep the heart beating regularly Investigation into the Effect of pH on Enzyme Activity - Method - correct answer 1) Put a drop of iodine solution into every well of a spotting tile
- Place a Bunsen burner on a heatproof mat, & a tripod & gauze over the Bunsen burner. Put a beaker of water on top of the tripod & heat the water until it is 35°C - keep the temperature of water constant throughout the experiment
- Use a syringe to add 1cm³ of amylase solution and 1cm³ of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the tube into the beaker of water & wait for 5 minutes
- Next, use a different syringe to add 5cm³ of a starch solution to the boiling tube
- Immediately mix the contents of the boiling tube & start a stopwatch
- Use continuous sampling to record how long it takes for the amylase to break down all of the starch - use a dropping pipette to take a fresh sample from the boiling tube every 30 seconds & put a drop into a well. When the iodine solution stays browny-orange, starch is no longer present
- Repeat the experiment with the buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down Calculation - Rate of Reaction - correct answer Rate = 1000/time Benedict's Test - testing for sugars - correct answer 1) Prepare a food sample & transfer 5cm³ to a test tube
- Prepare a water bath so that it's set to 75°C
- Add some Benedict's solution to the test tube (about 10 drops) using a pipette
