AQA GCSE Biology - Organisation

What is a tissue?

A tissue is a group of cells with a similar structure and function.

What is an organ?

An organ is a group of tissues working together for a specific function.

What are organ systems?

Organ systems are groups of organs which work together to form organisms.

What is the function of the digestive sytem?

- break down large molecules of food into smaller, soluble ones so that they can be absorbed into the bloodstream

What is the function of the mouth in the digestive sytem?

- food is chewed
- amylase enzymes released by the salivary glands begin to digest starch

What is the function of the stomach in the digestive sytem?

- protease enzymes begin the digestion of proteins

- contains hydrochloric acid which provides the optimal pH conditions for the protease

- churning turns the food into a fluid which increases the SA for enzymes to digest

What is the function of the pancreas in the digestive sytem?

- pancreas releases amylase and protease enzymes into the SI which continue the digestion of starch and protein, and begin the digestion of lipids

What is the function of the liver and gall bladder in the digestive sytem?

- releases bile into the SI
- gall bladder stores bile

What is the function of the SI in the digestive sytem?

- walls of the SI release enzymes to continue the digestion of protein and lipids

- here, small food molecules are absorbed into the bloodstream

What is the function of the LI in the digestive sytem?

- here, water is absorbed into the bloodstream

What is the function of the rectum and anus in the digestive sytem?

- rectum stores faeces
- faeces is released from anus

What happens to the products of digestion after?

- products used by the body to build new carbohydrates, lipids, and proteins

- some of the glucose produced is used in respiration

What is the function of enzymes?
What are enzymes?

Enzymes catalyse (speed up) chemical reactions.
Enzymes are protein molecules.

How do enzymes work?

Enzymes have an active site where only a specific substrate fits into. The enzyme then breaks down the subtrate into the products.

Enzymes lower the activation energy.

What is the enzyme and substrate theory called?

The 'lock and key theory' shows that enzymes are specific and the substrate must fit perfectly into the active site.

What are proteins broken down into?

What happens after the products are absorbed into the bloodstream?

Proteins (chains of amino acids) are broken down into amino acids by protease.

When the amino acids are absorbed by the body cells, they are joined together in a different order to make human proteins.

What are carbohydrates broken down into?
What is the specific case for starch?

Carbohydrates (chain of simple sugars) are broken down by carbohydrases into simple sugars.
Starch is broken down by amylase.

What is the structure of lipids?

What are lipids broken down into?

A lipid molecule consists of a glycerol molecule attached to 3 fatty acid molecules.

Lipids are broken down by lipase enzymes into glycerol and fatty acids.

What are the 2 functions of bile?

- bile emulsifies lipids (increase SA => increase rate of lipid breakdown)

- the alkaline bile also neutralises the HCL to provide the optimum conditions for lipase enzymes => increases rate of lipid digestion

What happens if we increase the temperature for enzymes? Why?

- activity of the enzyme increases and the reaction is faster because the enzyme and the substrate are moving faster, colliding more frequently

What happens at the optimum temperature?

enzymatic reactions occurring at maximum possible rate
- maximum frequency of successful collisions

What happens if we increase the temperature past the optimum? Why?

- enzyme activity rapidly decreases to zero and active site is denatured
- at high temperatures, enzyme vibrates and the shape of the active site changes so substrate no longer fits

How can we test for starch?

* Take the food sample and grind with distilled water using a mortal & pestle; transfer paste to a beaker, add more distilled water, stir to dissolve; filter

1) Add 2cm3 of food solution to test tube.
2) Add a few drops of iodine solution.
3) If starch, iodine: orange => blue-black

How can we test for reducing sugars?

*

1) Add 2cm3 of food solution to a test tube.
2) Add 10 drops of Benedict's solution.
3) Place tube into beaker and half-fill with hot water from kettle, leave for 5min.
4) If sugar, Benedict's solution: blue => green/yellow/brick-red

How can we test for proteins?

*

1) Add 2cm3 of food solution to a test tube.
2) Add 2cm3 of Biuret solution.
3) If protein, Biuret solution: blue => purple/pink

How can we test for lipids?

* but without filtering

1) Add 2cm3 of food solution to a test tube.
2) Add 3 drops of Sudan III.
3) Shake test tube gently to mix.
4) If lipids: red-stained oil layer will separate out and float on surface

Why should no naked flames be present when testing for lipids?

Sudan III contains ethanol which is flammable.

Describe a method to investigate the effect of pH on amylase.

1) Place 1 drop of iodine solution into each well of a spotting tile.

2) In the first test tube, add 2cm3 of starch solution.

3) In the second test tube, add 2cm3 of amylase solution.

4) In the third test tube, add 2cm3 of pH5 buffer solution.

5) Place all 3 test tubes in a water bath (30°C) for 10min to allow the solutions to reach the correct temperature.

6) Combine the 3 solutions into 1 test tube and mix with a stirring rod. Return test tube to the waterbath and start a stopwatch.

7) After every 30s, use the stirring rod to transfer 1 drop of solution into a spotting tile well.

8) Iodine should turn blue-black if starch is present.

9) Stop transferring when the iodine remains orange. (reaction complete). record this time.

10) Repeat whole experiment with different pH buffers.

What are some problems with thi method and how could we solve this issue.

- samples taken every 30s (only have an approximate time for when the reaction is complete) => take samples every 10s

- not obvious when iodine does not turn blue-black => ask several people to look at the spotting tile to decide the time => mean

How is the small intestine adapted for absorption of food molecules?

- length of 5m => very large SA

- interior covered with millions of VILLI => increase SA
- microvilli on the surface of villi
- very good blood supply from capillaries => rapidly removes the products of digestion (maintains high concentration gradient)
- thin membrane (short diffusion pathway)

What is the problem of having a single circulatory system?

Blood loses a lot of pressure so blood reaches organs relatively slowly => cannot deliver a great deal of oxygen

What is advantageous about a double circulatory system?

Blood passes through the heart twice which repressures it so it reaches organs quickly.

What is, and what is the function of the heart?

The heart is an organ, consisting mainly of muscle tissue, that pumps blood around the body.

What is the order of the 4 chambers in the heart? (left to right on a diagram)

Right Atrium > Left Atrium > Right Ventricle > Left Ventricle

How are the atria separated from the ventricles?

By atrioventricular valves

What is the flow of blood through the heart?

The vena cava brings in deoxygenated blood from the body.

The blood passes from the heart to the LUNGS in the pulmonary Artery, where the blood becomes oxygenated.

Oxygenated blood passes from the LUNGS to the heart in the pulmonary veIN.

Oxygenated blood is pumped from the heart to the body in the aortA

What is the role of valves?

Valves prevent the backflow of blood.

Why does the left side of the septum have a thicker muscular wall than the right side?

The left ventricle has to pump pump to the entire body so it requires a greater force from the thicker muscular wall.

What is the function of coronary arteries?

The coronary arteries branch out of the aorta to supply the heart muscle with oxygen so it can be used in repiration to provide the energy for contraction.

How is the natural resting heart rate controlled?

What happens if this stops working correctly?

By a group of cells located in the right atrium that act as a pacemaker.

If the pacemaker becomes faulty, docotrs can implant an artifical pacemaker to correct irregularities in the heart rate.

What do arteries do?

How are they adapted for this?

Arteries carry very high pressure blood Away from the heart to the organs in the body.

- very thick muscular walls to withstand the very high pressure
- elastic fibres which stretch to cope with the blood surges pass through (then recoil in between to keep the blud moving)

What do capillaries do?

How are they adapted for this?

Capillaries are where substances such as glucose and oxygen diffuse out to the cell in the organs (carbon dioxide diffuses back into the blood).

- very thin walls (short dffusion pathway for rapid substance diffusion)

What do veins do?

How are they adapted for this?

VeINs carry low pressure, slow-moving blood back to the heart.

- have valves to prevent backflow of slow-moving blad
- thin wall (thick = unecessary)

What is the plasma?

What is its function?

The plasma is the liquid part of the blood?

The blood plasma transports dissolved substances around the body, such as:
- soluble digestion products (small intestine => other organs)
- carbon dioxide (organs => lungs)
- urea (liver => kidneys)

What is the function of red blood cells?

Red blood cells transport oxygen from the lungs to the body cells.

How are red blood cells adapted to their function?

- contain haemoglobin which binds to oxygen in the lungs
- no organelles => more room for haemoglobin
- biconcave disc shape => increase surface area => oxygen diffuses in and out rapidly

What is the function of white bood cells?

White blood cells form part of the immune system.

What features help white blood cells to carry out their function?

- do have a nucleus (contains DNA which encodes the instructions for their job)

What is the function of the platelets?

Platelets are tiny fragments of cells that help the blood to clot.

What can donated blood be used for in medicine?

- to replace blood that has been lost during an injury
- platelets are extracted to help patient with blood clotting
- proteins that are extracted from blood can be useful, e.g. antibodies

What are some problems with donating blood?

- in a blood transfusion, the donated blood has to be the same blood type as the patient's (otherwise the patient's immune system could reject the blood)

- risk of infection (different diseases could be transmitted via blood)

What are cardiovascular diseases?

Diseases of the heart and blood vessels.

What does it mean if cardiovascular diseases are non-communicable?

- they are not infectious (cannot be passed from person to person)

What happens if someone has coronary heart disease?

Layers of fatty material build up inside the coronary arteries, narrowing them, and therefore, reduce the flow of blood through the coronary arteries.

=> heart muscle receives less oxygen to use in respiration
=> muscle cannot contract efficiently

What are statins?

- pros?

- cons?

- STATINS ARE DRUGS which reduce the level of cholesterol in the blood

- they slow down the rate that fatty materials build up
- reduce the risk of coronary heart disease

- do have some unwanted side-effects, e.g. liver problems

What are stents?

- pros?

- cons?

A STENT is a tube which can be inserted into to the coronary artery to keep it open

- blood can flow normally throught the coronary artery

- stent will not prevent other regions of the coronary arteries from narrowing
- does not treat the underlying causes of the disease

What happens if heart valves are faulty and do not fully open?

What happens if heart valves are leaky?

The heart has to pump extra hard to force the blood through
=> causes heart to enlargen

If the heart valves are leaky, the patient can feel weak and tired

What 2 treatments are used for faulty heart valves?

- replacement with an artificial, MECHANICAL valve (made from metal)

- replacement with a biological valve from an animal, e.g. piggo

What are the pros and cons of mechanical valves?

- can last a lifetime

- may increase the risk of bloodclots => patients have to take anticlotting drugs

What are the pros and cons of biological valves?

- do not need to take drugs

- do not last as long and may need to be replaced

What is heart failure?

Heart failure is the inability of the heart to pump sufficient blood to meet the needs for oxygen and nutrients.

What are the 2 problems associated with a donated heart to treat heart failure?

- not enough donated hearts available
- patient must take drugs to stop the donated heart from being rejected by the immune system

What is an artifical heart used for?

What are the disadvantages of using an artifical heart?

- temporary solution to heart failure while waiting for a heart transplant
- allow damaged heart to rest

- increase the risk of blood clotting, not a long-term soltuion to heart failure

What is the pathway of air in the gas exchange system?

Air passes into the lungs through TRACHEA > trachea now splits into two smaller BRONCHI (one bronchus to each lung) > bronchi dubdivide into many smaller bronchioles > alveoli

What is one key feature of the trachea?

- contains RINGS OF CARTILAGE prevent the trachea from collapsing during inhalation

What is the function of the alveoli?

Alveoli are the tiny air sacs within our lungs where oxygen diffuses in and carbon dioxide diffuses out from the bloodstream.

How are alveoli adapted for gas exchange?

- millions of alveoli (huge SA)

- very thin walls (short diffusion pathway)

- very good blood supply (maintains steep concentration gradient)

- moist (gases have to be dissolved to diffuse)

- ventilation brings in fresh oxygen ad removes carbon dioxide (maintains steep concentration gradient)

===> rapid rate of gas diffusion

What is key about the control of mitosis?

- extremely tightly controlled (genes tell cells when to divide and when to stop dividing)

How are cancers formed?

Changes take place in the genes => uncontrolled growth and division => produces a tumour (aka growth)

What is the difference between benign and malignant tumours?

- benign tumours are growths of abnormal cells found in one area (usually contained within a membrane)
- lack the ability to invade other parts of the body; they stay in one place

- malignant cells invade neighbouring tissues and move into the bloodstream and spread to form new, secondary tumours
- cancer

What are the risk factors linked to cancer?

- genetics

- lifestyle

- exposure to carcinogens

Why is radon a carcinogen?

Radon releases ionising radiation which damages the DNA in our cells (causes cells to undergo uncontrolled cell division) => increases risk of developing lung cancer

What is a communicable disease? Give an example.

What is a non-communicable disease? Give an example.

A communicable disease can be spread from person to person, e.g. measles.
- spread by pathogens

A non-communicable disease cannot be spread from person to person, e.g. coronary heart disease.

What is health?

What can ill health be caused by?

Helath is the state of physical and mental well-being.

Ill health can be caused by:
- both communicable and non-communicable diseases
- poor diet
- high levels of stress
- life situations

What is TB?

Why may some people be unable to fightoff the bacteria that cause TB?

Tubercolosis (TB) is a fatal, communicable lung disease.

Some people have a defective immune system, e.g. people with AIDs (caused by HIV), so they are more likely to suffer from infectius diseases like TB.

How can cervical cancer be caused by another disease?

The human papilloma virus (HPV) infects the cells of the cervix, triggering cancer.

How can allergies be caused by a pathogen?

Allergies, such as asthma or dermatitis, can be triggered by immune reactions initially caused by a pathogen, which the immune system fights off, but is left with an allergy.

Give an example where a mental illness can be caused by a physical illness?

Depression can be caused by arthritis.

What is epidemiology?

The study of the patterns of disease to determine risk factors.

Why doesn't a correlation prove a cause?

A correlation does not prove that a disease is caused by a risk factor; it only suggests that they might be linked.

What is a causal mechanism?

What is the correlation between cigarette smoking and lung cancer?

What is the causal mechanism between cigarette smoking and lung cancer?

A causal mechanism is evidence that a risk factor definitely leads to a particular disease.

Cigarette smoking and lung cancer have a positive correlation; this shows that they may be linked.

Cigarette smoke contains carcinogens which damage DNA and increase the risk of cancer.

What is the problem of only sampling a group of people?

How can we avoid bias when sampling?

You cannot try to draw conclusions from this small group of people to the whole population.

To avoid bias:
- take sample as LARGE as possible
- take sample as RANDOM as possible

What are the risk factord for cardiovascular diseases?

- a diet high in fat and low in vegetables => increases certain types of cholesterol in the blood => increases rate that fatty materils build up in the arteries

- a diet high in salt => increases blood pressure

- smoking => increases risk

- regular exercise => decreases risk

What are the risk factors for lung cancer and other diseases of the lungs?

- smoking increases risk of lung cancer (contains carcinogens) but also other lung diseases like emphysema

What is the effect of smoking during pregnancy?

What is the effect of drinking alcohol on an unborn baby?

- smoking when pregenant increases risk of miscarriage & premature birth

- drinking alcohol when pregnant can cause fetal alcohol syndrome (children may have learning difficulties and other mental/physical problems)

What other diseases are also caused by drinking alcohol?

Adults who drink alcohol excessively increase their risk of liver cirrhosis & liver cancer.

- can also affect the brain
=> addiction
=> memory loss

What are the risk factors of type 2 diabetes?

- obesity increases risk

What is the risk factor of lung cancer that is not linked to lifestyle?

- radon is a radioactive gas which damages the DNA in cells

What is the top and bottom of the leaf covered with?

What is the function of both these layers?

The top and bottom of the leaf are covered with a layer of very
thin epidermal cells which form epidermal tissue
- upper & lower epidermis

- The epidermises protect the top and bottom surfaces of the leaf

What is the key adaptation of the upper epidermis?

- transparent => allows light to pass through to the photosynthetic cells below

What is the function of the waxy cuticle?

The thin, oily waxy cuticle reduces the evaporation of water from the surface of the leaf => helps prevent leaf from drying out

What is the function of the stomata?

- stomata allow carbon dioxide to diffuse into the leaf and oxygen to diffuse out

- stomata also help to control the amount of water vapour that can pass out of the leaf (when water is lost, guard cells become flaccid, stoma closes)

What is the palisade mesophyll?

The palisade mesophyll is a layer that consists of palisade cells.

What is the function of the palisade cells?

The palisade cells contain many chloroplasts (containing chlorphyll) that absorb the light energy needed for photosynthesis.

What is the function of the spongey mesophyll?

The spongey mesophyll is full of air spaces which allow CO2 to diffuse from the stomata uo through the spongey mesophyll to the palisade cells to be used in photosynthesis (vise versa for O2).

What is the function of the xylem?

Xylem tissue transports water and dissolved minerals from the roots to the stem and leaves.

What is the function of the phloem?

Phloem tissue transports dissolved sugars produced by photosynthesis from the leaves to the rest of the plant.
- translocation

Where can meristem tissue be found?

What is the function of the meristem tissue?

We find meristem tissue at growing tips in roots and shoots.

The meristem tissue contains stem cells which can differentiate into different types of plant tissue at any point in the plant's life.

What is transpiration?

What is the transpiration stream?

Why is the transpiration steam important?

Transpiration is the constant evaporation of water from the surfaces of leaves.

evaporation of water from cells > water vapour diffuses through air spaces and out of the leaf through stomata > water passes from the xylem into the leaf to replace the lost water > water is drawn into the root air cells and up the xylem vessels to the leaf

The transpiration stream is important because:
- water is needed for photosynthesis
- dissolved mineral ions (such as magnesium) are required in the plant
- evaporation of water cools the leaf down

What factors lead to a high rate of transpiration?

- higher temperatures => molecules moving faster
- dry conditions (not humid) (maintain a steep concentration gradient outside the leaf)
- higher wind speed => water is removed away outside the leaf quickly (maintain steep concentraction gradient)
- higher light intensity => increases the rate of photosynthesis => stomata open to allow CO2 to enter (water can then pass out)