GCSE AQA Biology - Organisation

5 Levels of Organisation

Cell, Tissue, Organ, Organ System, Multicellular Organism

Cells

The basic building blocks of life.

Tissue

A group of similar cells that work together to perform a specific function.

Organ

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

Organ Systems

A group of organs that work together to perform a specific function.

Enzymes

Biological catalysts.

Lock and Key theory

• Substrate binds to enzyme active site with a complementary shape

• The enzyme catalyses the breakdown of the substrate

Substrate

The substance an enzyme acts on.

Factors affecting rate of enzyme-catalysed reaction

Temperature and pH

Amylase

Breaks down starch into simple sugars.

Where is amylase made? (3)

Salivary glands, pancreas, small intestine

Protease

Breaks down proteins into amino acids.

Where is protease made? (3)

Stomach (as pepsin), pancreas, small intestine

Lipase

Converts lipids into fatty acids and glycerol.

Where is lipase made? (2)

Pancreas and small intestine

Where is bile produced, stored and released?

• Produced in the liver

• Stored in the gall bladder

• Released into the small intestine

Bile function

• Neutralises hydrochloric from the stomach, making conditions alkaline for enzymes

• Emulsifies fats to increase their surface area for digestion

Salivary glands

Produce amylase in saliva.

Stomach

• Churns food

• Produces protease

• Produces hydrochloric acid

Hydrochloric acid function (2)

• Kills bacteria

• Provides optimum pH for protease

Gall bladder

Stores bile before releasing it into the small intestine.

Pancreas

Produces protease, amylase and lipase and releases them into the small intestine.

Small intestine

Produces enzymes to complete digestion and absorbs digested food into the bloodstream.

Large intestine

Absorbs excess water and food.

Rectum

Stores faeces before it is excreted by the anus.

Test for sugars

• Add benedict’s solution to food sample in hot water bath.

• Positive result - blue to green/yellow/brick-red

Test for proteins

• Add biuret solution

  Positive result - blue to purple

Test for starch

• Add iodine solution

• Positive result - brown/orange to blue/black

Test for lipids

• Add ethanol solution

• Positive result - colourless to cloudy

Where does air move when breathing in?

Through the mouth/nose, down the trachea, into the bronchi, through the bronchioles and into the alveoli.

Adaptations for gas exchange

• Rich blood supply (steep concentration gradient)

• Large Surface area

• Thin walls

Double circulatory system (2)

• Right ventricle pumps deoxygenated blood to the lungs for oxygen

• Left ventricle pumps oxygenated blood around the body

How does the heart pump blood?

• blood flows into the atria from the vena cava and the pulmonary vein

• blood is contracted into the ventricles which contract blood into the pulmonary artery or the aorta and out of the heart

Pacemaker

Controls heart rate by producing small electrical impulses to surrounding muscle tissue, causing them to contract.

Artificial pacemaker

A device that controls heartbeat if the natural pacemaker does not work.

Artery

Carries blood away from the heart (high pressure)

Artery adaptations (2)

• Thick muscular and elastic walls to withstand high pressure

• Small lumen

Vein

Carries blood into the heart (low pressure)

Vein adaptations

• Valves prevent backflow of blood

• Thin walls

• Wide lumen

Capillary

Carries blood to tissues and cells and connect arteries and veins.

Capillary adaptations (2)

• One cell thick wall - short diffusion path

• Very narrow lumen

Blood

A tissue consisting of plasma, in which the red blood cells, white blood cells and platelets are suspended.

Red blood cells

Carry oxygen from the lungs to all the cells in the body.

Red blood cell adaptations

• Contain lots of haemoglobin (bind to oxygen)

• Biconcave shape

• No nucleus

White blood cells

Defend against infection

Platelets

Clot blood at the sight of a wound to prevent blood pouring out and microorganisms getting in.

Plasma

carries blood cells and platelets around the body

Cardiovascular disease

Disease of the heart or blood vessels.

Coronary heart disease

Coronary artery is blocked by layers of fatty material building up, narrowing it and restricting blood flow.

Stents

Tubes inserted into the coronary artery that keep them open, allowing blood to flow.

Advantages of stents (2)

• Lower the risk of a heart attack

• Effective for a long time

Disadvantages of stents (2)

• Requires surgery - risk of complications and infection

• Risk of blood clot near stent

Advantages of statins (3)

• Reduce risk of strokes, coronary heart disease and heart attacks

• Increase amount of beneficial cholesterol

• May prevent other diseases

Disadvantages of statins (3)

• Long term drug - must be taken regularly

• Negative side effects

• Effect isn’t instant

Artificial heart

A mechanical device that pumps blood for a person with a faulty heart.

Advantages of artificial heart (3)

• Less likely to be rejected

• Keeps patient alive while waiting for a donor heart or allow heart to rest

• Reduce need for donor heart

Disadvantages of artificial heart (4)

• Requires surgery

• Not as effective as natural hearts

• Risk of blood clots and strokes

• Patient must take drug to thin their blood

Risk of faulty valve (2)

• Allows blood to flow in both directions

• Blood doesn’t circulate as effectively

Advantage and disadvantage of valve replacement (2)

• Less drastic procedure than heart transplant

• Surgery - problems with blood clots

Upper epidermis

Single layer of cells that protects against water loss and allows light to pass

Waxy cuticle

Reduces water loss

Palisade mesophyll

Tightly packed cells with lots of chloroplasts to absorb light for photosynthesis.

Spongy mesophyll

Contains lots of air spaces to increase rate of diffusion of gases.

Stomata

Allow diffusion of carbon dioxide into the plant for photosynthesis and oxygen out.

Guard cells

Control the opening and closing of stomata

How does the stomata open?

• When the plant has plenty of water the guard cells become turgid

• Inner cell wall is very thick, so doesn’t stretch as much as the thinner outer cell wall, causing the guard cells to curve away from each other.

Xylem

Carries water for photosynthesis and mineral ions from the roots to the stem and leaves.

Xylem characteristics (3)

• Made of dead cells joined together with no end walls between them

• One way transport

• Walls strengthened with lignin

Transpiration

The movement of water from the roots, through the xylem and out of the leaves.

Translocation

The movement of dissolved sugars from the leaves to the rest of the plant

Phloem

Transports dissolved sugars made in leaves during photosynthesis to the rest of the plant for immediate use or storage.

Phloem characteristics (2)

• Transport goes in both directions

• Cells have end walls with small holes to allow substances to flow through

How does higher temperature affect transpiration?

Increases transpiration because water evaporates faster.

How does higher light intensity affect transpiration?

Increases transpiration because the stomata opens wider to let more CO2 in for photosynthesis.

How does lower humidity affect transpiration?

Increases transpiration because the drier the air, the steeper the concentration gradient of water between the inside and outside of the leaf.

How does faster wind speed affect transpiration?

Increases transpiration because the water vapour is removed quickly, maintaining a steep concentration gradient.