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In order of increasing complexity, what are multicellular organisms made of?
Cells → tissues → organs → organ systems
Organelle
A specialised unit within a cell which performs a specific structure
Cell
The basic building block of all living organisms
Tissue
A group of cells working together to perform a shared function, and often with a similar structure
Organ
A structure made up of groups of different tissues, working together to perform specific functions
Organ systems
A group of organs with related functions, working together to perform certain functions within the body
What must organisms take in from the environment for their survival?
Food
Water
Oxygen
Other essential substances
What must plants take in from the environment for their survival?
Carbon dioxide for photosynthesis
What else must organisms do for their survival?
To remove waste substances
What do small organisms do with essential and waste substances?
Exchange them between themselves and the environment over their body surface. Simple chemical substances can diffuse in and out of their bodies.
What defines how quickly an organism can absorb substances?
Surface Area
What defines how much of a substance an organism needs?
Volume
What happens to the Surface Area as the Volume increases?
SA increases, but not at the same rate (increases slower).
What is the problem with SA’s slower increase as volume increases? What does the organism do to rectify this?
There is insufficient surface area to absorb substances and meet their needs. This is why organisms have developed body systems that add additional absorbing area to exchange surfaces.
What is the problem of an organism’s volume increasing to quickly? What does the organism do to rectify this?
Diffusion is not quick enough to move substances to where they’re needed in the organism’s body. This is why organisms have developed transport systems.
What increases the effectiveness of exchanging surfaces in plants and animals?
Having a large surface area
Having a short distance for diffusion
What are examples of organisms’ adaptations to increase their surface area?
flattened shape of structures eg. leaves
alveoli in the respiratory system
villi in digestive system
What are examples of organisms’ adaptations to decrease the distance required for diffusion?
membranes of cells
flattened shape of structures eg. leaves
walls of blood capillaries are 1 cell thick
the epithelia of alveoli (in respiratory system) and the villi (in small intestine) are only 1 cell thick
What additional adaptations for effective exchange surfaces do animals have?
Efficient blood supply to transport molecules to and from the exchange surface.
What are examples of this efficient blood supply adaptation in animals?
Network of blood capillaries surrounding each alveolus in the lungs
Network of blood capillaries in each villus in the small intestine
Ventilation
The process of breathing in and out, bringing air to and removing air from the exchange surface (the alveoli).
The moving blood and ventilated surfaces means…
This…
A steep concentration gradient can be maintained. This increases effective exchange.
The human lungs are an exchange surface which are adapted for…
Absorbing oxygen (needed for respiration) into the blood from the air.
Transferring carbon dioxide (produced by respiration) from the blood into the lungs, then the air.
The lungs are organs enclosed within the _____ or _____.
Chest
Thorax
What surrounds the lungs?
12 pairs or ribs
What moves the ribs?
2 sets of intercostal muscles
What is below the lungs?
a muscular diaphragm
diaphragm
A large sheet of muscle that separates the lungs from the abdominal cavity.
What are the lungs sealed by?
2 airtight pleural membranes, wrapping around the lungs and lining the ribcage.
What is the Trachea also commonly known as?
the windpipe
The trachea branches into…
2 bronchi - 1 bronchus to each lung.
Where are the ‘rings of cartilage’ in the body?
inside the walls of the trachea
What do the rings of cartilage in the trachea do?
They help to keep the trachea open as air is drawn in.
The bronchi split into…
smaller branches, and then into smaller tubes called bronchioles.
Each bronchiole ends in…
a cluster of microscopic air sacs called alveoli.
What does the exchange of gases occur between?
alveoli
blood in the capillaries (that supply the lungs)
How much of the outside of the alveoli is covered by capillaries?
over 70%, providing a large surface area for gases to diffuse across.
diagram of the network of capillaries surrounding the alveoli…
diagram of gas exchange
alveoli adaptations (4)
small size - around 300 μm in diameter - to give it a large SA:V ratio
number - there are around 350 million alveoli in each lung
thin walls - one cell thick
alveoli are lined with a thin film of moisture as gases dissolve in this water, making the diffusion path even smaller.
Both of these adaptations aim to provide a very large surface area and a short diffusion path for more effective gas exchange.
What is the total surface area of the alveoli?
70 square metres
What does the increased blood flow through the surrounding capillaries of the alveoli mean?
Gasses are being removed continually, and steep concentration gradients are set up for gases to diffuse.
What do the diaphragm and ribcage do during ventilation (breathing)?
They move to create a lower air pressure in the lungs than that of the air outside the body. This means air rushes into the lungs.
What is therefore the most important muscle for breathing?
The diaphragm, with the external intercostal muscles being the 2nd most important.
Breathing is a ______ process resulting from…
passive
pressure changes in the lungs.
When breathing in…
Diaphragm contracts and pulls downwards
Intercostal muscles contract and pull ribs upwards and outwards
Volume of thorax increases so pressure decreases, and air is drawn into the lungs
When breathing out…
Diaphragm relaxes and moves up
Intercostal muscles relax and the ribs move downwards and outwards
Volume of thorax decreases so pressure increases and air leaves the lungs
What exchange surface do fishes use?
Gills
Why do fishes need a different type of exchange system (gills)?
Because water is capable of holding only low concentrations of oxygen.
How does ventilation work in fishes?
Water flows in through the mouth.
The water flows over the gills.
The water leaves through the operculum.
Gill filaments in fish - diagram
How does water flow through the gills?
Water flows over the gills in the opposite direction of blood flow (counter current flow). This means exchange of oxygen and CO2 is more efficient than if the water and blood were both flowing in the same direction.
Why is exchanges of gases very efficient in fish?
large SA of gills
large SA of blood capillaries in each gill filament
short diffusion distance - outer layer of gill filaments and capillary walls are just 1 cell thick
efficient ventilation of gills with water (counter current flow of water and blood)
The moving blood and ventilated gill surfaces means…
Gases are continually removed - oxygen enters the blood, and CO2 is removed to the water. Also, high concentration gradients can be maintained.
Is gas exchange more difficult for fish or land animals?
fish
Why is gas exchange more difficult for fish than for land animals?
The concentration of oxygen in water is dependent on the temperature of the water, while there is always 21% of oxygen in the air at any temperature.
What is the concentration of oxygen in 15°C water?
1%
What do the low percentages of oxygen in water mean for fish?
The efficiency of their gills is very high; 70-80% of the available oxygen is extracted from the water.
What are the main nutrients humans need in large quantities?
Carbohydrates
Proteins
Lipids (fats)
We get these by consuming them.
What happens when the foods containing these nutrients are broken down?
Our body reassembles them into its own carbohydrates, proteins and lipids.
Why are these nutrients reassembled?
because…
Most of the molecules in food are too large to pass through the absorbing surface of the gut wall.
The carbohydrates, proteins and lipids are reassembled in the form required four our bodies, rather than other animal or plant versions.
What is the major function of carbohydrates?
Carbohydrates are a source of energy, and glucose is the main respiratory substrate.
What are the major sources of carbohydrates?
Starch: potatoes, rice and wheat products
Bread
Cereals and Pasta
Sugars: fruit, smoothies, fizzy drinks, chocolate and sweets
What is the major function of proteins?
growth and repair
What are the major sources of protein?
Meat
Cheese and Eggs
Beans
Nuts and Seeds
What is the major function of lipids?
For energy, and to make up part of our cell membranes, meaning they are essential for normal growth.
What are the major sources of lipids?
Butter and Margarine
Meat and processed Meat
Plant oils
Oily fish
Nuts and Seeds
Carbohydrates in our diet include…
…sugars and starches.
sugar
A simple carbohydrate that is sweet to the taste.
starch
A type of carbohydrate.
Plants can turn glucose (from photosynthesis) into glucose for storage, and turn it back into glucose when it is needed for respiration.
Why is the size of the glucose molecule important?
It is small enough to be absorbed directly through the walls of the digestive system.
Starch is a ______ of ______.
Starch is a polymer of glucose.
Cellulose is made up of…
…glucose molecules.
What is cellulose used for?
It makes up the plant cell walls. This means it is a fundamental part of our diet.
Cellulose can / cannot be broken down by our digestive system.
What does this mean?
cannot
This means that instead of being broken down, it is egested from the gut.
egestion
The process of passing out the remains of food that has not been digested, as faeces, through the anus.
What happens to the glucose molecules once they are absorbed by the body?
They are transported to the cells and…
used for respiration.
reassembled into the storage form of carbohydrate in animals - glycogen.
What happens to glucose molecules in plants?
Glucose produced by photosynthesis is inverted into starch for storage, and cellulose, for cell wall synthesis.
In humans and animals, glucose is stored in ______, not converted into _____.
glycogen
starch
What are proteins made of?
Amino Acids
Can proteins pass through the gut wall?
No - they are molecules too large to pass through the gut wall, so they must first be broken down into animo acids.
Once inside the body, what do the amino acids do?
They are reassembled into the proteins the individual requires - the process of protein synthesis.
Where are excess amino acids broken down?
in the liver
Lipids are…
…esters of fatty acids and a glycerol.
esters
A type of organic compound formed in the reaction between an alcohol and a carboxylic acid.
Can lipid molecules pass through the gut wall?
No - they must be digested first.
What are lipids used for inside the body?
The lipid are reassembled into the lipids the cell needs, for instance, the cell membranes.
Test for Sugars
Benedict’s solution
Heat in a water bath to above 60
Negative → Positive
Green → Yellow → Orange → Red
Colour depends on how much glucose present
Test for Sugars - Hazards
Wear safety goggles.
Benedict’s solution is an irritant.
Avoid contact with skin and eyes.
Test for Starch
Iodine solution
positive: blue-black
negative: remains orange-brown (no change)
Test for Starch - Hazards
Wear safety goggles
Iodine solution is an irritant
Avoid contact with skin and eyes
Test for Proteins
Biuret Solution and mix
positive: lilac-purple
negative: blue (no change)
Solution may turn completely purple or develop a purple ring between the layers, but both of these indicate a positive result.
Test for Proteins - Method
Add 1cm³ of biuret solution A to the food solution.
Mix the liquids.
Add 1cm³ of biuret solution B and shake.
Test for Proteins - Hazards
Wear safety goggles.
Biuret solution A is corrosive.
Biuret solution B is an irritant.
Avoid contact with skin and eyes,
Test for Lipids
Ethanol (few drops) and food mixed and added to separate tube of water
Shake
positive: cloudy white emulsification
negative: colourless (no change)
Test for Lipids - Hazards
Wear safety goggles
Ethanol is flammable
Avoid contact with skin and eyes
What are the 2 functions of the human digestive system?
To break down complex food substances
To provide a very large surface area for maximum absorption of food
What are the regions of the digestive system?
Mouth
Salivary Glands
Oesophagus
Liver
Gall Bladder
Stomach
Pancreas
Small Intestine
Large Intestine
Appendix
Anus
Bold - food passes through this organ.
What are the 2 new organs we are discovering?
Duodenum
Ileum
The duodenum and ileum are within the…
…small intestine.
Note 
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