AQA GCSE Biology Higher Paper 1

Eukaryotic cells = Complex cells that include all animal and plant cells. A eukaryote is an organism made of eukaryotic cells.

Prokaryotic cells = Smaller and simple. e.g. bacteria. A single-celled organism.

Animal cells - Contain a nucleus (containing genetic material and cell activity), cytoplasm (where chemical reactions happen and containing enzymes), cell membrane (holding the cell together and controlling incomes and outcomes), mitochondria (aerobic respiration, transferring the needed energy), and ribosomes (where proteins are made).

Plant cells = Contain all features of an animal cell, alongside a cell wall (made of cellulose which supports the cell and strengthens it), a vacuole (containing sell sap), chloroplasts (where photosynthesis happens, containing chlorophyll, makes food and absorbs light for the cell).

Bacteria cells = contain cytoplasm, cell membrane, cell wall, a strand of DNA and plasmids (small rings of DNA).

Electron microscopes = Using electrons instead of light. Higher magnification.

Magnification = Image Size / Real Size

PRACTICAL

1) Clip the prepared slide onto the stage of the microscope.

2) Move the stage up until it's in full focus from the eyepiece. Adjust the focus if need be to get a clear image.

3) Draw observations with a pencil.

Differentiation = The process by which a cell changes to become specialised for its job. As cells change, they develop different subcellular structures to do specific functions. 

e.g. Sperm Cells - Reproduction. Gets the male DNA to the female DNA to the female DNA. It has a long tail and a streamlined head to help it swim to the egg. Lots of mitochondria for energy. It also carries enzymes to digest through the egg cell membrane. 

e.g. Nerve Cells - Rapid signalling. Carries electrical signals from one part of the body to another. These cells are long and have branched connections to connect to other nerve cells and form a network. 

e.g. Root Hair Cells - Absorbing water and minerals. on the surface of plant roots, which grow into long hairs that stick out into the soil. This gives the plant a big surface area for absorbing water and mineral ions from the soil.

e.g. Phloem and Xylem Cells - Form tubes which transport substances such as food and water around plants. Long and joined end to end. Hollow in the centre so that things can flow through.

Chromosomes = Lengths of DNA molecules contained in the nucleus. Each chromosome contains a large number of genes controlling the development of different characteristics. Body cells have two copies of each chromosome - one from the mother, one from the father. 23 pairs of chromosomes from a human cell.

Mitosis - Body cells dividing to produce new (from damaged) cells. 

The Cell Cycle

1) In a non-dividing cell, the DNA is all spread out in long strings. Before it divides, the cell grows the amount of subcellular structures such as mitochondria and ribosomes. 

2) The cell's DNA duplicates - so there's one copy for each cell. The left arm has the same DNA as the right arm of the chromosome.

3) The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of the chromosome go to opposite ends of the cell.

4) Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells. Lastly, the cytoplasm and the cell membrane divide. 

Binary fission = Where the cell splits into two. This is the process:

1) The circular DNA and plasmids replicate.

2) The cell gets bigger and the circular DNA strands move to the opposite ends of the cell.

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

4) The cytoplasm divides and two daughter cells are produced - each having one copy of the circular DNA, but have a variable number of copies of the plasmids.

Bacteria can divide very quickly if given the right conditions  (e.g. a warm environment). If conditions become unfavourable, then the cells will stop dividing and eventually die. 

Calculating mean division time = Make sure both times are in the same units. Divide the total time that the bacteria are producing cells by the mean division time. Multiply 2 by itself for the number of divisions to find the number of cells.

You can investigate the effect of antibiotics on bacterial growth.

1) Place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria.

2) The antibiotic should soak into the agar jelly. Antibiotic-resistant bacteria will continue to grow but non-resistant strains will die.

3) Make sure you soak it in sterile water so that any difference between the growth of the bateria around the control disc and the antibiotic discs s due to the effect of the antibiotic alone. 

4) Leave the plate for 48 hours at 25 degrees C.

5) The more effective the antibiotic is against the bacteria, the larger the inhibition zone will be.

Make sure UNCONTAMINATED CULTURES are used to avoid the growth of pathogens.

Stem Cells = Undifferentiated cells which can divide to produce a lot more stem cells. They're found in human embryos, and they have the potential to turn into any cell in which they're instructed to. 

Adults have stem cells, but they're only found in certain places and can only turn into certain cells.

Uses of Stem Cells

- Medical: Stem cells can be used to replace faulty cells in sick people, i.e. inserting insulin-producing cells for people with diabetes and more. RISK: Stem cells can be contaminated in the lab and be passed onto the patient to make them even sicker.

AGAINST STEM CELL RESEARCH: Each embryo cell is a potential human life, but others think that curing existing patients who are suffering is more important than the rights of embryos. Other sources of stem cells can be used as a compromise.

Diffusion = The spreading out of particles from an area of higher concentration to an area of lower concentrations. The bigger the concentration gradient, the faster the diffusion rate. 

E.g. perfume particles being diffused into the air, so they spread out.

Cell membranes hold the cell together, but they also let things in and out., usually by diffusion - substances such as oxygen, amino acids, glucose and water. Big molecules like starch and proteins CAN'T fit through the membranes. 

Just like diffusion in the air, particles flow through the cell membrane from where there's a higher concentration to where there's a lower concentration. 

The larger the surface area of the membrane, the faster the diffusion rate as more particles can pass through at once.

Osmosis = The movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.

A partially permeable membrane = One with very small holes in it. 

During osmosis, the water molecules pass both ways through the membrane as they move about randomly all the time. 

Because there are more water molecules on one side than the other, there's a steady net flow of water into the region with fewer water molecules. The water tries to even up the concentration either side of the membrane.

Root hair cells grow into hairs which stick out into the soil, with each branch being covered in millions of microscopic hairs. This gives the plant a large surface area for absorbing water and mineral ions from the soil. Plants need this for healthy growth - they can't use diffusion to pick up the minerals from the soil.

Active transport = Allows the plant to absorb minerals from a very dilute solution against a concentration gradient - essential for growth. But active transport needs energy from respiration to make it work. 

We need active transport to stop us starving - it's used in the gut when there's a power concentration of nutrients in the gut, but a higher concentration of nutrients in the gut, but a higher concentration of nutrients in the blood. 

Cells can use diffusion to take in substances they need and get rid of waste products. I.e:

- 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. 

How easy it is for an organism to exchange substances depends on the organism's Surface Area : Volume ratio.

Gas exchange in the lungs - it transfers oxygen to the blood and removes waste carbon dioxide from it, using millions of little air sacs called alveoli. The alveoli are specialised to maximise the diffusion of O2 and CO2 - they have an enormous surface area, a moist surface lining, very thin walls and a good blood supply. 

Villi - The inside of the small intestine is covered in millions and millions of these tiny little projections called villi. They increase the surface area in a big way so that digested food is absorbed much more quickly into the blood. They have a single layer of surface cells, and a very good blood supply to assist quick absorption.

Tissues - a group of similar cells that work together to perform a function.

E.g. the muscular tissue (moves the stomach wall to churn up the food), glandular tissue (makes and secretes chemicals like enzymes and hormones), epithelial tissue (covers some parts of the body e.g. the inside of the gut).

Organs - A group of different tissues that work together to perform a function. 

E.g. The stomach is made of the muscular tissue (moves the stomach wall to churn up the food), the glandular tissue (makes digestive juice to digest food), and the epithelial tissue (covers the outside and inside of the stomach).

Organ systems - A group of organs working together to perform a function.

E.g. the digestive system - consists of the glands (produces digestive juices), the stomach and small intestine (which digest food), the liver (produces bile), the small intestine (absorbs soluble food molecules) and the large intestine (absorbs water from undigested food to leave faeces).

Living things produce enzymes that act as biological catalysts - reducing the need for high temperatures and we only have enzymes to speed up useful chemical reactions in the body.

Biological Catalysts - A substance which increases the speed of a reaction, without being changed or used up in the reaction.

Enzymes are all large proteins made of amino acid chains, which fold into unique shapes for the function.

Every enzyme has an active site with a unique shape that fits onto the substance involved in a reaction, If the substrate doesn't match the enzyme's active site, then the reaction won't be catalysed.

A higher temperature increases the rate at first, although if it's too hot then some of the bonds holding the enzyme together will break, changing the shape of the active site.

The pH also affects enzymes if it's tooo high or low - the PH interferes with the bonds holding the enzyme together, changing the shape.

Starch, proteins and fats are big molecules - too big to pass through the walls of the digestive system, so enzymes break them down into smaller ones such as sugars, amino acids, glycerol and fatty acids. These smaller and soluble molecules can pass through the walls of the digestive system and also be absorbed into the blood. 

E.g. amylase (carb) - breaks down starch into maltose (a sugar). Amylase is made in three different places; the salivary glands, the pancreas, and the small intestine.

E.g.  proteases - breaks down protein into amino acids. Proteases are made in three places; the stomach, the pancreas and the small intestine.

E.g. lipases - breaks down lipid into glycerol and fatty acids. Found in two places; the pancreas and the small intestine. 

Bile neutralises the stomach acid and emulsifies (breaks it down into tiny droplets) fats - the hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is an alkaline, so it neutralises the acid and makes conditions alkaline.

- Salivary glands: Produce amylase enzyme in the saliva.

- Gullet: Oesophagus.

- Liver: Where bile is produced, and it neutralises stomach acid and emulsifies fats.

- Gallbladder: Where bile is stored, before it's released into the small intestine.

- Large intestine: Where excess water is absorbed from the food.

- Small intestine: Produces proteases, amylase and lipase enzymes.

- Pancreas: Produces protease, amylase and lipase enzymes before releasing them into the small intestine. 

- Stomach: Pummels the food with the muscular walls. Produces the protease enzyme and pepsin. Also produces hydrochloric acid for two reasons: killing bacteria and giving the right pH to protease.

Sugars - Benedict's Test.

1) Prepare a food sample and transfer 5cm to a test tube. 2) Prepare a water bath set to 75 degrees 3) Add some Benedict's solution using a pipette 4) Place the test tube in the water bath using a test tube holder and leave it there for 5 minutes 5) Colours should change from the blue to a green, yellow or red depending on how much sugar.

Starch - Iodine Solution

1) Make a food sample and transfer 5cm of the sample to the test tube. 2) Add a few drops of iodine and shake - if it contains starch the colour will change from light brown to black/blue.

Proteins - Biuret Test

1) Prepare a sample of your food and transfer 2cm of your sample onto a test tube. 2) Add 2cm of biuret solution to the sample and gently shake it. 3) It will change from blue to pink or purple if it contains proteins.

Lungs are in the thorax - separated from the lower part of the body by the diaphragm. Protected by the ribcage, surrounded by the pleural membranes. Two tubes called bronchi go to the lungs as they take in air. Bronchi split into progressively smaller tubes called bronchioles. They end at small bags called alveoli.

Alveoli - Air sacs surrounded by a network of blood capillaries - this is where gas exchange  happens. The blood passing into the alveoli contains a lot of carbon dioxide and very little blood. Oxygen diffuses out of the alveolus and into the blood, and vice versa with carbon dioxide (so it can be breathed out).

When the blood reaches the body cells, oxygen is released from the red blood cells (when there's a high concentration) and diffuses into the body cells (where there's a low concentration). 

Vice versa with carbon dioxide - it diffuses out of the body cells (high concentration) into the low-concentrated blood. It's then carried back to the blood.

Circulatory system - The heart, blood vessels and the blood. There are two circuits:

- First one: Right ventricle pumps deoxygenated blood to the lungs to take in oxygen, before returning to the heart.

- 2nd: The left ventricle pumps deoxygenated blood around all the other organs around the body. The blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heart to be pumped out of the lungs again.

The Heart = Heart is a pumping organ that keeps the blood flowing around.

1) Blood flows into the two atria from the vena cava and the pulmonary vein.

2) The two atria contract, pushing blood into the ventricles.

3) The ventricles contract, forcing the blood into the pulmonary artery and out of the heart.

4) The blood flows to the organs through arteries and returns through the veins.

5) The atria fill again and the whole cycle starts over.

There are three different types of blood vessel: arteries (carry blood away from the heart), capillaries (these are involved in the exchange of materials at the tissues) and veins (carry blood to the heart).

Arteries = Pumps the blood out at high pressure so the artery walls are strong and elastic. Thick walls. Thick layers of muscle to make them strong and elastic fibres to allow them to stretch and spring back.

Capillaries = Arteries branch into capillaries. Very small. Carry the blood really close to every cell in the body to exchange substances with them. Permeable walls so substances can diffuse in and out. Supply food and oxygen. One cell thick; this increases the rate of diffusion by decreasing distance.

Veins = Capillaries eventually join up to form veins. Blood's at the lower pressure in the veins so the walls aren't as thick as artery walls. Bigger lumen to help blood flow despite lower pressure. They also have valves to keep the blood in the right direction.

- Red blood cells carry oxygen from lungs to all cells in the body. Large surface area for absorbing oxygen. No nucleus - allows room to carry oxygen. Contain haemoglobin. 

- White blood cells defend against infection. Shape up to take unwelcome microorganisms in a process called phagocytosis. Others produce antibodies to fight microorganisms as well as antitoxins to neutralise any toxins produced by microorganisms. Contain a nucleus.

Platelets and blood clots: Small fragments of cells. No nucleus. They stop blood pouring out and to stop microorganisms getting in. Lack of platelets result in bruises and excessive bleeding.

Plasma = The liquid that carries everything in blood. Contain red and white blood cells and platelets. Contain nutrients like glucose and amino acids. Also contain carbon dioxide, urea, hormones, proteins and antibodies.

- Coronary heart disease: when the coronary arteries that supply the blood to the muscle of the heart get blocked by layers of fatty materials. This makes the arteries narrow, so blood flow is restricted and there's a lack of oxygen to the heart muscle - resulting in a heart attack. 

Stents = tubes outside arteries. They keep them open, making sure blood can pass through to the heart muscles. They're an effective way of lowering the risk of complications i.e. a heart attack in people with coronary heart disease.

Cholesterol = An essential lipid that your body produces and needs to function properly. Too much of cholesterol can cause health problems i.e. fatty deposits. Statins are drugs that can reduce the amount of cholesterol.

Advantages of statins: Reduces the risk of strokes/coronary heart diseases,  increases the amount of beneficial type of cholesterol, prevents some other diseases.

Disadvantages of statins: Long-term drug so people could forget, negative side effects, isn't instant.

Two types of tumours:

1) Benign - Where the tumour grows until there's no more room. The tumour stays in one place rather than invading other tissues. Usually not dangerous and not cancerous.

2) Malignant - Where the tumour grows and spreads to neighbouring healthy tissues. Cells can break off and spread to other parts in the bloodstram. Malignant cells can invade healthy tissues elsewhere in the body from secondary tumours. Cancerous.

Risk factors include - Smoking, obesity, UV exposure (radiation), viral infection (e.g. infection with hepatitis B can increase the risk of liver cancer).

Sometimes you can have faulty genes which make you more susceptible to cancer, e.g. mutations in the BRCA genes. (Think of Sonia on EastEnders lol)

Epidermal Tissue - this covers the whole plant, covered by a waxy cuticle which helps to reduce water. (Lower epidermis is full of little holes called stomata which can let CO2 diffuse directly into the leaf).

Palisade mesophyll tissue - Where photosynthesis happens (contains chloroplasts which are at the top of the leaf to absorb light)

Spongy mesophyll tissue - contains big air spaces to allow gases to diffuse in and out of cells. Air spaces increase the rate of diffusion.

Xylem and phloem - transport water, mineral ions and food around the plant. They form a network of vascular bundles, which deliver water and other nutrients to the entire leaf and take away glucose.

Meristem tissue - the growing tips of shoots and roots and can differentiate into different plant cells.

Pathogens = Micro-organisms that enter the body and cause disease.

Bacteria = Small cells which can reproduce rapidly inside your body. They can make you feel ill by producing toxins that damage cells and tissues.

Viruses (NOT cells) = Tiny. They can reproduce rapidly inside your body to produce many copies of themselves. The cell will then burst, releasing all the new viruses. Cell damage.

Protists = Single-celled eukaryote. Some protists are parasites, living on or inside other organisms and can cause them damage. Often transferred to the organism by a vector (doesn't get the disease itself.

Fungi = Some are single-celled, others have a body made up of hyphae. The hyphae can grow and penetrate human skin and the surface of plants, causing diseases. Can produce spores which is spreadable.

Pathogens can be spread in different ways e.g. Water (contamination e.g. cholera), air (pathogens can be carried in the air and then inhaled), or Direct Contact (contaminated surfaces).

Spreading of disease can be reduced or prevented. For example:

1) Being hygienic - Washing hands thoroughly to prevent pathogens infecting other people.

2) Destroying vectors - By getting rid of the organisms that spread disease, you can prevent it being passd on. E.g. insects being killed using insecticides or by destroying their habitat.

3) Isolating infected individuals - Isolating an infected individual will prevent it being spread to anyone else.

4) Vaccination - People won't be able to develop the infection and then pass it on to someone else.

Antibodies are produced by B-lymphocytes (a type of white blood cell).

Monoclonal antibodies are produced from lots of clones of a single white blood cell, thus all antibodies are identical and will only target one specific protein antigen. 

Lymphocytes do not divide easily. 

B-lymphocytes + tumour cells = Hybridoma

Different cells in the body have different antigens on their cell surface, so you can make monoclonal antibodies that will bind to specific cells in the body. Cancer cells have antigens on their cell membranes that aren't found on normal body cells (tumour markers).

An anti-cancer drug can be attached to these monoclonal antibodies - this could be a radioactive substance, a toxic drug or a chemical. These antibodies are given to patients through a drip, targeting specific cells. The drug kills cancer cells but doesn't kill any normal body cells.

RISKS: Can cause side effects e.g. fever, vomiting.

Guard cells have a kidney shape which opens and closes the stomata in a leaf.

When the plant has lots of water, the guard cells fill with it and go plump. This makes the stomata open so gases can be exchanged for photosynthesis. 

When the plant is short of water, the guard cells lose water and become flaccid, making the stomata class. This helps stop too much water vapour escaping.

Thin outer walls and thickened inner walls make the opening and closing work.

Sensitive to light and close at night to save water without losing out on photosynthesis.

Adapted for gas exchange and controlling water loss within a leaf.

Pre-clinical tests: Drugs are tested on human cells and tissues in the lab. Although, no human cells and tissues are used to test drugs that affect whole or multiple body systems e.g. testing a drug for blood pressure may be used on an animal as it has an intact circulatory system.

Testing drugs on animals: This tests efficacy, to find out about its toxicity and to find the best dosage. Some find it cruel on live animals although some think it's important to make sure it's safe.

Human volunteering:

1) First, the drug is tested on healthy volunteers to make sure there are no harmful side effects when the body's working normally. Should the results be good, the drugs can be tested on people suffering from the illness. The optimum dose is found.

2) Patients are randomly put into two groups. One is given the new drug, the other is given a placebo (a substance that's like the drug being tested but doesn't do anything). This is so the doctor can see the difference the drug makes.

3) Clinical trials are blind - not even the doctor nor the patients know whether they receive either the drug or the placebo.

Anaerobic Respiration = When you do vigorous exercise and your body can't supply enough oxygen to your muscles, they start doing anaerobic respiration as well as aerobic respiration.

Glucose --> Lactic acid 

Anaerobic respiration does not transfer nearly as much energy as aerobic respiration. This is because glucose isn't fully oxidised.

Investigating respiration

You can measure breathing rate by counting breaths, and heart rate by taking the pulse.

You could take your pulse after sitting down for 5 minues, then again after 5 minutes of gentle walking, 5 minutes of slow jogging, then after running for 5 minutes.

The more intense the exercise is, the bigger the pulse rate as your body needs to get more oxygen to the muscles and take more carbon dioxide from the muscles. Recommended to do it as a group and plot the average pulse rate for each exercise.