Organisms exchange surfaces

What is the relationship between SA:V ratio and the size of an organism

The larger an organism, the smaller the SA:V ratio

How do small organisms e.g. unicellular transport substances

• they have a smaller SA:V ratio so they can simply exchange by diffusion due to their short diffusion pathway

What effect does SA:V have on metabolism

smaller organisms lose heat faster so they have a higher rate of metabolism and respiration

What is different in exchange in larger organisms

• they have larger SA:V ratio

• This means they require special adaptations such as alveoli due to their demand of a higher metabolic rate and efficient waste transport

How does gas exchange happen in unicellular organism

• they have a short diffusion pathway from the centre of the cell from the cell membrane

• They have a large SA:V ratio

• Photosynthesis and respiration ensure a concentration gradient

What do insects have for gas exchange

They have a tracheal system with spiracles, trachea and tracheoles

How does oxygen move into cells in an insect via diffusion

• air with oxygen diffuses down spiracles, down trachea then tracheoles to the cells

• This is driven by the concentration gradient provided when the cells respire

• CO2 leaves via spiracles

How does gases move into insect by mass transport

The insect contracts and relaxes abdominal muscles to move gases on mass

Describe abdominal pumping

The rhythmic relaxing and contracting of abdominal muscle which increases or decreases the volume and pressure of the abdomen so O2 or CO2 moves in or out down the pressure gradient

How does gases move into insects while flying

• the muscle cells respire anaerobically which produces lactate

• This lowers water potential of cells, causing water to move out of tracheoles into cells

• This decreases the volume of trachea so air is driven in

What are the adaptations of the tracheal system (4)

• tracheoles have thin walls so short diffusion pathway

• Highly branched so large SA

• Diffusion of gases through air is very fast

• Larger insects have abdominal pumping which maintains concentration gradient

How are insects adapted to prevent water loss

• waterproof coating

• Spiracles have valves which open and shut which prevent excessive water loss

• Reduces SA:V ratio where water evaporates

What is a fish’s gas exchange system

• They have four layers of gils made up of gill filaments covered in lamellae

• They have a counter current flow to maintain concentration gradient

Describe the counter current flow

• blood flows in opposite direction of water

• So, blood is always next to water with high oxygen concentration so oxygen rapidly diffuses in

• The countercurrent flow ensures that an equilibrium isn’t reached and there is a concentration gradient

• It maintains this concentration gradient along whole lamellae

What are the adaptations of the gills (4)

• many lamellae to provide large surface area

• Thin epithelium + capillary network in each lamellae for short diffusion pathway

• Ventilation of gills provides high oxygen water to maintain concentration gradient

• Replacement of deoxygenated blood with oxygenated blood via circulatory system maintains concentration gradient

How does gas exchange occur in plants

• palisade calls use CO2 for photosynthesis which creates a diffusion gradient

• The cO2 diffuses into stomata then air spaces then into these cells

  • The CO2 can also diffuse in from adjacent mitochondria

What are the adaptations plants have for gas exchange (4)

• Many stomata for large SA

• Air spaces allow large SA

• Large SA:V ratio for higher rate of diffusion

• Thin leaves for short diffusion distance

What are xerophytes

plants found in areas of little water

What are the adaptations of xerophytes (4)

• thicker waxy cuticle = prevent uncontrolled evaporation

• Small leaf SA = reduces area for evaporation

• Low stomatal density = smaller SA for diffusion

• Sunken stomata and hair = reduces water potential gradient

How to measure surface area of leaf

• Draw around leaf on graph paper

• Count the number of squares inside the drawing

• Multiply the answer by two to get the surface area of both the top and bottom sides

What is the path air takes to the alveoli

Mouth → trachea → bronchi → bronchioles → alveoli

Describe gas exchange in mammals

• there is a high concentration of oxygen in alveoli

• Oxygen diffuses down concentration gradient across alveoli epithelium and capillary endothelium

• Oxygen associates with haemoglobin to make oxyhaemoglobin for transport

What are the adaptations of gas exchange of mammals

• squamous, one cell thick cells so short diffusion pathway

• Lots of folded alveoli for large surface area

• Good circulation and ventilation for maintaining concentration gradient

How does inspiration work

• external intercostal muscles contract and internal relax which lifts ribcage up and out

• Diaphragm contracts and flattens

• This increases volume of thoracic cavity and lowers pressure below atmospheric pressure

• Air moves in down pressure gradient

How does expiration work

• external intercostal muscles relax and external contract which moves ribcage down and in

• This relaxes diaphragm and it becomes dome shaped

• This decreases volume of thoracic cavity and increases pressure above atmospheric pressure

• Air moves out down pressure gradient

What is tidal volume

Volume of air per breath

What is breathing rate

Number of breaths per minute

What is pulmonary ventilation

Volume of air that enters lungs per minute

How to calculate pulmonary ventilation

Pulmonary ventilation = tidal volume x breathing rate (dm³)

What is the purpose of digestive enzymes

They break down large insoluble substrate to soluble products which can be absorbed into the bloodstream and assimilate into bloodstream

What are the stages of breaking down carbohydrates

Starch to maltose to glucose

How is starch broken down

Starch → maltose via amylase

Where is amylase found

• salivary glands

• Pancreas

How is maltose broken down

Maltose → glucose via maltase

Where is maltase found

membrane bound disaccharidase found on cell membrane of epithelial cells in small intestine

What is the first stage of breaking down proteins

Endopeptidase hydrolyse peptide bonds within protein which makes smaller chains and increase surface area

What is the second stage of breaking down proteins

Exopeptidase hydrolyse peptide bonds at ends of proteins

What is the third stage of breaking down proteins

Dipeptidase (exopeptidase) hydrolysis dipeptides into amino acids

Where are exopeptidase and endopeptidase found

• stomach

• Small intestine

Where are dipeptidase found

Membrane bound dipeptidase found in the cell membrane of epithelial cells in small intestine

How are aminos acids absorbed into small intestine

• cotransport

• Na+ ions actively transported from cell into capillary using ATP, creating concentration gradient

• Cotransport protein binds Na+ with amino acids and they diffuse in via facilitated diffusion

• Amino acids go back into capillary via facilitated diffusion

What is the process of lipid breaking down

Tryglyceride → monoglyceride + 2 fatty acids via lipase

What are bile salts used for

They emulsify large lipid molecules to smaller droplets to increase surface area

What happens to the smaller lipid droplets

Lipase digest these into smaller drops called micelles

How are micelles absorbed

• micelles move towards cell membrane of epithelial cells as they are soluble

• Fatty acids and monoglycerides are lipid soluble so they move across membranes

• They then reform into tryglycerides in smooth endoplastic reticulum or Golgi

What is mass transport

The bulk transport of molecules around the body

Describe the structure of haemoglobin

• 4 polypeptide chains so quaternary structure

• Has a haem group (Fe2+) which binds with oxygen

When does oxygen associate with haemoglobin

• in a high partial pressure of oxygen as it has a high affinity

  • The lungs

Where does oxygen dissociate with haemoglobin

• where there is a low partial pressure as it has a low affinity

What does high affinity mean

Combines with oxygen more readily

What does low affinity mean

Releases oxygen more readily

Why is the oxygen dissociation curve this shape

Cooperative binding which means it difficult for the first oxygen to bind but once it does, the tertiary structure of the haemoglobin changes which uncovers another binding site which makes it easier for a second oxygen to bind

Where does haemoglobin have high affinity

At the lungs

Where does haemoglobin have low affinity

At the respiring cells

What is the Bohr effect

The oxygen dissociation curve shifts to the right, lowering affinity, allowing for more oxygen to be dissociated for more respiration for more ATP

Why does the Bohr effect happen

• when respiring, CO2 produced which lowers the pH of the blood which changes the tertiary structure of proteins and enzymes as it breaks hydrogen bonds

Where else is the curve shifted to the right

In Animals with a higher metabolic rate so higher rate of respiration

In what cases does the curve shifted to the left

Animals who live in areas with low oxygen leads to the curve shifting to the left

Why is the curve shifting to the left beneficial to animals who live in areas with low oxygen

• haemoglobin has a higher affinity for oxygen

• Oxygen more readily associates

• Enough oxygen for more respiration

What is the cardiac muscle

The thick muscular walls of the heart which are myogenic and doesn’t fatigue with oxygen

What is the coronary artery

Supplies the heart with oxygen and it branches off the aorta

What are the atria

They have thinner muscular walls with weaker contractions as it only pumps blood to the ventricles

What are the ventricles

They have thicker muscles for bigger contractions as they withstand higher pressure as blood flows to the lungs and body

Why is the right ventricle thicker than the left

• left = thicker muscles for larger contractions due to higher pressure as it pumps blood to whole body

• Right = bit thinner as it prevents damage to capillaries and for slower flow to allow gas exchange

What is the vena cava

Carries deoxygenated blood from the body to the heart

What is the pulmonary vein

Carries oxygenated blood from the lungs to left atrium

What is the pulmonary artery

carries deoxygenated blood from right atrium to lungs

What is the aorta

Carries oxygenated blood from left ventricle to the rest of the body

Describe the cardiac cycle (5)

• blood flows from the vena cava and pulmonary vein into the atria which increases its pressure moving blood passively into ventricle

• The atria contract and blood moves down pressure gradient to ventricles so the AV valves open as pressure is higher in the atria

• The atria relax but now the pressure in ventricles is now higher than atria so AV valves shut

• The ventricle contracts and there is now a higher pressure in the ventricles than the arteries so semi lunar valves open and blood passes into the aorta and pulmonary artery

• Ventricles relax and pressure in arteries are higher and semi lunar valves shut

Describe the graph

• B = closing AV valves

• C = opening semi lunar valves

• D = closing semi lunar valves

  • There is a small increase before the dip due to the elastic recoil of the artery which helps maintain blood pressure

• E = opening semi lunar valves

How to calculate cardiac output

Cardiac output = heart rate x stroke volume

• cardiac output = volume of blood leaving ventricle in one minute

• Heart rate = how long it takes for the heart rate to return to original

• Stroke volume = the range of the values

Why do mammals require a double circulatory system

• increase pressure and the rate of flow of bood

• To allow more O2 for more respiration

What are arteries

• carry blood away from heart

• Highest pressure as it carries blood from ventricles

What are arterioles

They join arteries to capillaries

What are capillaries

Blood vessels that allow the transport of substances

What are veins

They carry blood to the heart

• low pressure due to friction from blood flow and further away from ventricle

What are venules

They join veins with capillaries

Features of arteries

• thick muscular layer to prevent bursting under high pressure

• Thick elastic layer to maintain high pressure as it stretches when high and recoil when low

• Endothelium reduces friction

Features of arterioles

Thick muscular later to control flow as it contracts reducing blood flow by narrowing lumen which prevents damage to capillary

Features of capillaries

• one cell thick endothelial = short diffusion pathway

• Highly branched for large SA

• Narrow lumen to slow blood for more time for diffusion

• Pores between endothelial cells for tissue fluid

Features of veins

• thin elastic and muscle layer due to lower pressure

• Larger lumen

• Valves to prevent backflow of blood

What is tissue fluid

Fluid containing glucose, amino acids, fatty acids, ions and oxygen which bathes tissues

How is tissue fluid formed

• capillaries have small gaps so liquid and small molecules forced out

• As blood enters capillaries via arterioles, the smaller diameter causes a higher hydrostatic pressure sp small molecules such as glucose and water forced out

  • Ultrafiltration

What happens to the larger molecules in tissue fluid

They remain in the fluid

• Red blood cells, platelets, large proteins

How is tissue fluid reabsorbed

• large molecules lower the water potential

• At venule end, there is a lower hydrostatic pressure due to loss of liquid as well as a low water potential

• Water renters capillaries by osmosis down water potential gradient alongside waste products such as CO2

Why wont all liquid be reabsorbed by osmosis

Since an equilibrium will be reached

What happens to the rest of tissue fluid

They are absorbed by lymphatic system and they eventually drain back into bloodstream near heart

What is the role of the heart in tissue fluid production

• contraction of ventricles cause a high hydrostatic pressure

• This means that smaller molecules like water are forced out of capillary by ultrafiltration

What is transpiration

The loss of water by evaporation via stomata

What is transpiration affected by

• light intensity

• Temperature

• Humidity

• Wind

Wh does light intensity affect transpiration

• the higher it is, the more open stomata so there is a larger surface area for evaporation

Why deos temperature affect transpiration

The more heat, the more kinetic energy so there are faster molecules so there is more transpiration

Why does humidity affect transpiration

The more water vapour, the lower the water potential gradient so there is less evaporation

Why does wind affect transpiration

The higher the wind, the more water vapour blown away which maintains the concentration gradient so more evaporation

What are the adaptations of xylem

• hollow tubes with no living components for easier non restricted water flow

• No end walls to create a continuous column of water

• The side walls are strengthened with rings of lignin

• Pores allow movement between lignin

What is the effect of adhesion

It causes capillarity as when water molecules adhere to the xylem walls, it makes it narrower and capillarity forces water up the column

What is root pressure

When water moves into the roots by osmosis, there is now a higher pressure in the roots than the xylem so water moves into the xylem down a pressure gradient which aids the continuous column

Explain the water cohesion theory

• water lost from lead because of the evaporation of water from the mesophyll cells

• This lowers the water potential of mesophyll cells and pressure

• The water is pulled up xylem, creating tension and is pulled up via transpiration pull and negative pressure

• The water molecules stick together via cohesion via hydrogen bonds, forming a continuous column of water

• The water molecules adhere to the walls of xylem

What is the purpose of the potometer practical

Measures the rate of uptake of water in a time period which is proportional to transpiration

• it introduces one air bubbles and its distance is measured

Why is the sample cut underwater

To prevent air entering xylem and breaking the column