Organisation

Cells are the basic building blocks of all living organisms.

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

Organs are aggregations of tissues performing specific functions.

Organs are organised into organ systems, which work together to form organisms.

The Digestive System

the mouth both physically and chemically breaks down food

the oesophagus carries food from the mouth to the stomach

the stomach physically breaks down food by churning it, breaks down proteins and contains hydrochloric acid with a low pH to kill microbes in food so they don’t cause illness

the liver makes bile, which is alkaline to neutralise stomach acid. it also emulsifies fat into small droplets, increasing their surface area, making lipase more effective

the gall bladder stores and secretes bile

the pancreas makes enzymes

the small intestine absorbs nutrients via villi

the large intestine absorbs water from undigested food to produce faeces

enzymes

enzymes are biological catalysts, increasing the rate of reactions but not being used up. the way they work can be explained by the lock and key theory

1. the shape of the active site is specific and complementary to the substrate it can break down.

2. they collide and become attached, forming an enzyme-substrate complex

3. the enzyme catalyses the breakdown of the substrate and products are formed and released from the active site

enzymes require an optimum pH and temperature to work. at temperatures/pHs too far above/below the optimum, they will denature and their active site will change shape, meaning that the substrate can no longer fit and it cannot catalyse reactions.

Required Practical: food tests

Benedict’s reagent: add it to a food sample and heat in a water bath. should turn anywhere from blue to red depending on if and how much glucose is present

Iodine: add it to a food sample. it will turn from brown to a blue-black if starch is present

Biuret reagent: add it to food sample. will turn from blue to purple if protein is present.

Emulsion/ethanol: add ethanol to the food. shake to combine then pour into water. if the mixture goes cloudy, fats are present.

Sudan III: add to a mixture of food and water. a red layer will form on top if fats are present.

Required Practical: pH and amylase

Method

1. mark the spotting tile with time in the columns and pH on the rows

2. add a drop of iodine to each well of the spotting tile

3. use a water bath to heat a solution of starch, amylase and a buffer which maintain pH. water bath is used to maintain a constant temperature, where it could be a factor affecting rate.

4. at regular time intervals, something like every 30 seconds, transfer a drop of the solution to a well of the corresponding pH row.

5. if the iodine turns black, there’s starch present, and the amylase has denatured. so the faster the iodine stops seeing a change in colour, the faster amylase is breaking down starch so the faster the reaction and the more effective the enzyme at that pH

rate = product formed/reactant used / time

The heart

the heart pumps blood around the body in a double circulatory system. this means there are two circuits/routes for blood to flow.

1. deoxygenated blood

   • gets pumped in via the vena cava

   • right atrium contracts to force it into the right ventricle

   • AV valves close to prevent backflow

   • ventricle contracts, forcing blood into the pulmonary artery

   • it then travels to the lungs to get oxygenated

2. oxygenated blood

   • gets pumped in via the pulmonary vein

   • left atrium contracts to force it into the left ventricle

   • AV valves close to prevent backflow

   • ventricle contracts, forcing blood into the aorta

   • it travels around the body delivering oxygen to cells for respiration

blood vessels

arteries carry blood away from the heart.

they have thick muscular walls to make them strong and thick elastic layer that allows them to stretch to facilitate high blood pressure caused by the heart pumping

they have a narrow lumen (the hole in the blood vessel through which blood flows)

the blood in them is generally oxygenated, save for in the lungs, because this is where blood in them has their oxygen moved to veins to travel back to the heart and be circulated

veins carry blood towards the heart.

they have thin walls due to their large lumen that allows low pressure blood to flow through

they have valves to prevent backflow

the blood in them is generally deoxygenated, save for in the lungs, because this is where blood gets oxygenated and then travels back to the heart

capillaries carry blood close to the cells so substances can move between the two.

they’re one cell thick to make the diffusion pathway as short as possible, and thus the most efficient, and don’t have a muscular or elastic wall to facilitate this.

Blood

blood is a tissue made up of plasma, white blood cells, red blood cells and platelets.

1. plasma is the liquid that carries the other components of blood. it’s mostly water

2. white blood cells that protect the body from infection (see infection and response for specifics)

3. red blood cells that carry oxygen molecules from the lungs to the rest of the body by binding to it with haemoglobin

4. platelets which are essentially cell fragments that allow blood to clot, which can then dry into a scab that allows new skin growth underneath while keeping microorganisms out

Issues of the Heart

valves: can get damaged over time as they withstand a lot of pressure, so can get stiff and the heart becomes less efficient, or may develop a leak. biological (human and animal) or mechanical equivalents can be transplanted. biological valves work very well but degrade within 15 years while mechanical last for a long time but need to be medicated to prevent blood clots

artificial hearts are used to keep a patient alive while they’re awaiting a transplant

heart rate is controlled by a group of cells in the right atrium. this is known as your pacemaker. if there are irregularities with your heartbeat, an artificial pacemaker can be used.

coronary heart disease

coronary heart disease occurs when fatty material builds up in the coronary arteries that provide blood to the heart itself, and they become blocked. this means less blood flows to the heart, reducing its oxygen supply.

the oxygen supply to the heart needs to be maintained so that aerobic respiration can occur. the heart CANNOT start respiring anaerobically, because this produces lactic acid that causes muscle fatigue, and the heart cannot afford to tire and stop pumping blood, because the rest of you body cells will then stop respiring too.

there are 2 solutions:

1. stents - wire mesh tubes placed into the coronary arteries to hold them open, but you risk infection and blood clots

2. statins - drugs that lower cholesterol that leads to coronary heart disease. reduce risks but are only a preventative measure

The lungs

the trachea or windpipe sends air down into the lungs, where it then splits between the two bronchi which further split into bronchioles that lead to the alveoli

when you inhale, your ribcage moves up and out to facilitate an increase in chest volume, which results in low pressure. this causes air to be drawn into the lungs

when you inhale, gas exchange takes place.

1. alveoli fill with oxygen

2. blood in surrounding capillaries is deoxygenated as blood has flowed into them from pulmonary artery, and it has a lot of carbon dioxide

3. oxygen diffuses into the capillaries from the alveoli due to the concentration gradient

4. carbon dioxide diffuses into the alveoli from the capillaries

5. blood is now oxygenated and travels towards to heart via the pulmonary vein

alveoli are adapted to be as efficient for this diffusion as possible:

1. plentiful

2. small meaning they have a large surface area to volume ratio meaning diffusion occurs quicker

3. thin to make for a short diffusion pathway

other parts of the lungs are also adapted to make diffusion as efficient as possible:

1. capillaries are also only one cell thick, making for a short diffusion pathway

2. capillaries provide a good blood supply, removing oxygenated blood fast to maintain the concentration gradient

3. the action of breathing in and out maintains the concentration gradient

Health issues

health is a state of physical, mental and social wellbeing.

communicable diseases are infectious and caused by pathogens

non-communicable diseases aren’t passed on from person to person

diseases interact in a multitude of ways:

• someone with a weakened immune system is more likely to be infected with a communicable disease because the body is less able to fight off pathogens. they may be immunocompromised due to another disease

• infections by viruses in some parts of the body leads to cancers

• reduction in physical health can lead to a reduction in mental health

• immune responses due to infection can cause allergic reactions

non-communicable diseases can have huge financial and emotional impacts on the individual, their family and the wider community, with masses of people dying due to these diseases and, in some countries, healthcare not being free. it also has a nation-level impact because research into diseases and treatment is expensive. globally, there may be effects when a disease affects the working age population, in regards to productivity.

risk factors are things that increase the likelihood of having a non-communicable disease. they pertain to the person’s lifestyle, now and in the past. a few common ones are:

• diet

• obesity

• smoking

• drinking

• age

• genes

• sex

• infection

• carcinogens/ionising radiation

if one factor increases as another increases, they are correlated. a casual mechanism explains this correlation.

Cancer

cancer is the result of mutations in cells that leads to uncontrolled growth and mitosis.

benign tumours are growths of abnormal cells which are contained in one area, usually within a membrane. They do not invade other parts of the body.

malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours.

there are a few specific risk factors for different types of cancer:

• smoking

• obesity

• UV light (skin cancer)

• infection

• genes

Plant Tissues and Organ systems

meristem tissue differentiates to allow the plant to grow.

the leaf and gas exchange

epidermis tissue (upper and lower): covered with a waxy cuticle to reduce water loss by evaporation and make the plant waterproof

palisade mesophyll: site of photosynthesis. contains lots of chloroplasts and has a long vertical structure, at the top of the leaf, to maximise light received - long structure means that many of them can be lined up at top of the leaf

spongy mesophyll: air space that allows for diffusion of gases during gas exchange

guard cells: swell with water to cause the stomata to open, and lose water to close them

stomata: holes made by guard cells, that enable water loss (transpiration) and gas exchange when they're open. they’ll shut in certain conditions:

• when there’s little water: shut to prevent water loss

• when it’s night: photosynthesis can’t occur so there’s no point being open to let gas exchange occur and losing water

the leaf is the site of gas exchange in a plant, which enables photosynthesis, that generates the glucose and oxygen needed for respiration, which releases energy and enables the plant to carry out processes.

translocation

the movement of food substances made in the leaves up and down the plant via the phloem.

perforated cell walls (sieve plates) allows water and food (glucose) solution to pass between cells

hollow (bar cytoplasm) to facilitate movement of glucose - companion cells with mitochondria produce energy for the cell

transpiration

this is the loss of water from the leaves and stem as a result of gas exchange, when the stomata open. water is brought up into the plant via the root hair cells when they take up minerals, and is transported to the leaves by the xylem cells.

it’s affected by 4 main factors:

1. temperature - increases temperature makes water evaporate faster, so rate of transpiration increases

2. humidity - if it’s more humid there’s more water in the air, it’s more difficult for water to evaporate, so rate of transpiration decreases

3. light intensity - higher light intensity makes water evaporate faster, so rate of transpiration increases

4. air flow/wind - carries water away from the leaves, refreshing the concentration gradient and increases the rate of transpiration