Chemistry

Adaptations to facilitate exchange as this ratio reduces in larger organisms include changes to body shape and the development of systems

Larger organisms need a specialised surface / organ for gaseous exchange e.g. lungs - Because they have a smaller SA:V and a long diffusion pathway (and skin is waterproof / gas tight) -
As well as having a high demand for oxygen and to remove carbon dioxide

Adaptations of gas exchange surfaces shown by gas exchange... Across the body surface of a single-celled organism

Thin, flat shape - Large SA(:V) - Short diffusion pathway/distance (all parts of cell are a small distance away from exchange surfaces) - For rapid diffusion e.g. oxygen / carbon dioxide

Gas exchange of an insect

1. Air moves through spiracles (pores) on the surface of the insect
2. Air moves through tracheae
3. Gas exchange at tracheoles directly to/from cells - Oxygen diffuses down conc. gradient to respiring cell -
Carbon dioxide diffuses down conc. gradient from respiring cells

Adaptations of insects for efficient diffusion (gas exchange)

1)Large number of fine tracheoles which ensures large surface area

2)Walls of tracheoles are thin and short distance between spiracles and tracheoles so short diffusion pathway

3) Use of oxygen and production of co2 sets up a steep concentration gradient

3 methods of moving gases in the tracheal system

1) Gas can exchange by diffusion as when cells respire they use up oxygen and produce carbon dioxide , creating a concentration gradient from the tracheoles to the atmosphere.

2) The second method of gas exchange is mass transport in which an insect contracts and relaxes their abdominal muscles to move gases on mass

3) When the insect is in flight the muscles start to respire ANAEROBICALLY to produce lactate. This lowers the water potential of the cells and therefore water moves from the tracheoles into the cells by OSMOSIS. This decreases the volume in the tracheole and as a result more air from the atmosphere is drawn in.

Limiting water loss in insects adaptations

Water evaporates off the surface of terrestrial insects , and the adaptation of gas exchange provide ideal conditions for evaporation.

Insect adaptations to prevent water loss:
1) Insects have a small surface area to volume ratio where water can evaporate from
2) Insects have a WATERPROOF EXOSKELETON
3) SPIRACLES, where gases can enter and water can evaporate from , can open and close to reduce water loss.

Digestion and Absorption

Larger molecules are hydrolysed into smaller soluble ones .

Carbohydrates
Amylase hydrolyses starch into maltose, which is then broken down into maltase
1) Salivary amylase - produced by salivary glands
2) Pancreatic Amylase - produced by pancreas then secreted into the small intestine

Carbohydrate Digestion

Amylase is produced in the salivary glands released into the mouth
Amylase hydrolyses starch into maltose
digestion stops in stomach as pH is too acidic
- In pancreas , any starch is further digested
- In the ileum of small intestine MEMBRANE BOUND MALTASE hydrolyses maltose to glucose hydrolysing the glyosidic bond into membrane bound dissacharides

How are proteins digested?

Endopeptidase - hydrolyse peptide bonds between amino acids ( in the middle of the chain)

Exopeptidase - hydrolyse peptide bonds at ends of polymer chain

membrane bound dipeptidases - two amino acids are split

lipid digestion and absorption

Digested by lipase
Lipase produced in the pancreas, hydrolyses lipids into monoglycerides and fatty acids.

Bile salts produced in the liver and emulsifies lipids to form micelles which increases the surface area for lipase to work on
.
Micelles- vesicles formed of the fatty acids , glycerol , monoglycerides and bile salts

Absorption of Lipids - When micelles encounter the ileum epithelium cells (small intestine) , they can diffuse across the cell membrane as non-polar
Micelles get modified back into TRIGLYCERIDES in Rough Endoplasmic Reticulum and Golgi

The triglycerides combine with protein to form chylomicrons

The chylomicrons move into the lymph system by EXOCYTOSIS to be transported around the body

Adaptations of small intestine

Villi AND microvilli are folded which maxismise absorption by increasing the surface area.

Thin walls - short diffusion pathway

Network of capillaries which maintains the concentration gradient

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. ( 5 marks)

Micelles they contain bile salts and fatty acids. Make fatty acids more soluble in water.Fatty acids are absorbed by DIFFUSION. . Chylomicrons are formed then exocytosis occurs.

ATP Hydrolase Function

Releases energy ( atp - adp + pi) and allows ions to move against the concentration gradient.

Use your knowledge of lipid digestion to explain the differences in the
results for samples A and B shown in the table above.
You should assume that no absorption had occurred

1)Triglycerides decrease because of the action of lipase OR Fatty acids increase because of the action of lipase;

2. Triglycerides decrease because of hydrolysis (of
Fatty acids increase because of hydrolysis (of triglycerides);

3. Triglycerides decrease because of digestion of ester bonds (between fatty acid and glycerol) OR Fatty acids increase because of digestion of ester bonds (between

After collecting the samples, the scientist immediately heated them to 70 °C for 10 minutes. Explain why

To denature the enzymes/lipase; Accept description of denaturation in terms of change in tertiary structure.

2. So no further digestion/

Describe the role of micelles in the absorption of fats into the cells lining the ileum (3 marks)

Makes fatty acids more soluble

Brings fatty acids to the lining of the ileum

Fatty acids are absorbed by diffusion.

Describe the role of enzymes in the digestion of proteins in a mammal( 4marks)

Hydrolysis of peptide bonds


Endopeptidase act in the middle of protein/polypeptide

Exopeptidases act at end of protein/polypeptide

Dipeptidase acts on dipeptide/between two amino acids

Which enzymes are involved in the digestion of proteins?

Endopeptidases
Exopeptidases
Dipeptidases

Haemoglobin structure and function

Structure :
Has 4 polypeptide chains
Hemoglobin is a quaternary structure
Each haem group contains an Fe+ ion
Has 4 oxygen binding sites

Found in red blood cells (erythrocytes) - No nucleus - contain more haemoglobin -
Biconcave shape - increase surface area for rapid diffusion/absorption of oxygen

Red blood cells contains haemaglobin

Role of Haemaglobin:
Carrier of oxygen through blood to respiring tissues


When the first oxygen molecule binds to hemoglobin , it changes the hemoglobin shape it makes it easier for other oxygen molecules to bind so increasing the affinity.

What is affinity?

How readily / easily Hemoglobin can bind to oxygen.

How is oxygen loaded , transported and unloaded in the blood?

In the lungs, at a high pO2, haemoglobin has a high affinity for oxygen → oxygen readily loads / associates with haemoglobin

- At respiring tissues, at a low pO2, oxygen readily unloads / dissociates from haemoglobin - Also, concentration of CO2 is high, increasing the rate of unloading (Bohr effect - see further on)

oxygen dissociation curve

The Bohr Effect

When cells respire they produce co2 which raises the pco2
This increases the rate of oxygen unloading so lower affinity so the dissociation curve shifts to the right
The saturation of blood with oxygen is lower for a given po2 so more oxygen is released
This is called the Bohr Effect

What is oxyhaemaglobin?

Oxygen joins with haemaglobin to form oxyhaemaglobin
This is a reversible reaction as it can go from oxyhaemaglobin to haemaglobin

Cardiac Cycle

Atrial Systole
When both left atrium and right atrium both contract. Blood flows from the atria to the ventricles. The atrial pressure is always slow as atria has thin walls . The atria contracts and volume of blood in atria increases and ventricles relax. The pressure is higher in the atria than the ventricles. The Biscuspid valve OPENS and some blood moves into the ventricle.

Ventricular Systole
The ventricles contract and blood fills the ventricles and increases its volume and the atria relax the bicuspid valve CLOSES to prevent backflow of blood and pressure increases rapidly because of the thick muscular walls that contract. The pressure in the VENTRICLES is higher in the aorta and pulmonary artery which forces open the semi-lunar valves and blood is forced into these arteries.

Diastole
The ventricles and atria both relax
There is a higher pressure in the pulmonary artery and aorta closing the Semi - lunar valves to prevent backflow of blood into the ventricles.

What is the Bohr effect?

haemoglobins oxygen affinity is inversely proportional related to the conc of co2 in the blood

What do the different parts of the heart do?

Left Ventricle has a thicker muscular wall then the right ventricle as the left ventricle needs to pump blood around the body . The right ventricle only goes to the lungs

The ventricles have thicker walls than the atria because they need to push blood away from the heart whereas atria need to pump blood to a short distance to the ventricles.

The atrioventricular valves (AV) link atria and ventricles and stop blood flowing back into the atria when the ventricles contract.

The semi-lunar valves (SV) link ventricles to pulmonary artery and aorta and stop blood flowing back into the heart after ventricles contract

The cords attach to the atrioventricular valves to the ventricles to stop them being forced up into the atria when ventricles contract

Which ways do valves open?

Valves open in one direction
The atriventricular valves between atria and the valves and they open when the pressure in the atria is higher

SO valves open when pressure is greater before

Semi- lunar valve is between aorta and pulmonary artery
And the SL valve open when pressure is higher in the ventricles.

Structure of the heart need to finish

The human heart has 4 chambers of cardiac muscle - two atria and two ventricles