Exchange of Substances

Question 1

Talk about the role of the mouth in the digestive system.

Answer 1

The first stage of the digestive system where food is broken down into smaller pieces by chewing. This is an example of Mechanical Digestion. The teeth cut and crush the food. Its then mixed with saliva which is made in the Salivary Glands to form a ball of food called a bolus.

Chemical Digestion also occurs here- enzymes in the saliva begin to process the breakdown. The enzyme found in Saliva is called amylase. This is a type of carbohydrase that breaks down carbohydrates into maltose which can further be broken down into Glucose by maltase to be used as energy for processes like respiration.

Question 2

Talk about the oesophagus’ role in the digestive system.

Answer 2

long tube that connects the mouth to the stomach. Food is moved through the system by the process of peristalsis. The muscles in the wall of the oesophagus work together to produce wave-like contractions which have a squeezing-action that pushes the bolus through the gut.

Question 3

Talk about the Stomach’s role in the digestive system.

Answer 3

Mechanical- muscles in the stomach walls contract, churning the food and breaking it into smaller pieces.

Chemical- enzymes secreted from the stomach lining, as well as the pancreas, aid the breakdown of molecules. The main enzymes found are proteases: these digest proteins into amino acids.

The stomach also produces hydrochloric acid. This kills many harmful microorganisms that may have been swallowed along with the food. It also maintains the optimum ph. for the enzymes, which is in acidic conditions.

Question 4

Talk about the livers role in the digestive system.

Answer 4

The liver produces bile which helps emulsify fats into forms that can be absorbed called fatty acids. It also helps to neutralize stomach acid so its at an optimum PH for enzyme action.

Question 5

Talk about the Pancreas’ role in the digestive system.

Answer 5

Secretes pancreatic enzymes that break down molecules and also produces hormones such as glucagon and insulin which regulates the level of glucose in the blood.

Question 6

Talk about the small intestines (ileum’s) role in the digestive system.

Answer 6

A long muscular organ where food is further digested by enzymes produced by its walls and absorbs the products of digestion into the bloodstream to be used.

Question 7

What are some adaptations of the ileum?

Answer 7

Villi- foldings in the inner walls:
These increase surface area to volume ratio for maximum absorption and transport. it is further increased by millions of tiny projections on the villi called microvilli.
They have thin walls to reduce the overall distance over which diffusion takes place and are well supplied with blood to maintain a diffusion distance.

Question 8

Talk about the role of the large intestine and the rectum in the digestive system?

Answer 8

The large intestine absorbs excess water that has been passed through the digestive system which then leads to the rectum where the waste is stored before being remobed via the anus in excretion.

Question 9

What is the process of carbohydrate digestion?

Answer 9

1. Saliva from salivary glands enters the mouth whoch contains salivary amylase which starts hydrolysing any statcg in the food into maltose.
   2.The food enters the acidic stomach denaturing anylase and preventing further hydrolysis
2. Food is passed into the ileum where it mizes with pancreatic amylase to hydrolyse the remaining starch
3. Muscles in the intestine wall push food along the ileum where maltase on the epithelial lining hydrolyses the maltose into glucose.

This also happens with sucrose and lactose.

Question 10

What is the process of protein digestion?

Answer 10

Proteins are digested via proteases:
Endopeptidases- hydrolyses the peptide bonds between amino acids in the centre of proteins
Exopeptidases- Hydrolyses the peptide bonds on the terminal amino acids
Dipetidases- Hydrolyses the bonds between two amino acids of a dipeptide found on the surface of epithelial cells.

Question 11

Talk about Lipid digestion

Answer 11

Lipases hydrolyse lipids which are produced in the pancreas that hydrolyse the ester bond found in triglycerides.
1. Bile salts emulsify lipids into monoglcerides and fatty acids which stay associated with the salts forming micells.
2. When micells reasch the lining and release the products to easily diffuse accross the epithelial cells.
3. Once in the cells, they are recombined to form triglycerides in the endoplasmic reticulum.
4. In the Golgi, triglycerides are assosiated with cholestreol to form structures called chylomicrons which move out of the cell via exocytosis into capillaries.

Question 12

How are plants adapted for efficient gas exchange?

Answer 12

Stomata- open and close due to guard cells which allow gas to enter and leave the leaves
Air Spaces- Have a large surface area to volume ratio in the mesophyll for rapid diffusion.

Question 13

What are xerophytic plants and how are they adapted to water loss?

Answer 13

Stomata- sunken and contain stomatal hairs to maintain humid air for a concentraion gradient
Tick cuticle so less water can escape
Rolling of leaves- protects the lower epidermis from the outside and so that area becoms trapped with humid air so it has a high water potential.
Reduced leaf surface area reduces surface area to volume ratio so there is less area for stomata to talke up

Question 14

Talk about gas exchange in Fish.

Answer 14

Fish have a small surface area to volume ratio as well as a waterproof, gas-tight outer covering for gas exchange. Thus meaning that their surface is not adequate to supply and remove respitory gases so they have an internal sturcture.
Each gill is supported by an arch, along the arch there are multiple projections called gill filaments with lamellae on them which participate in gas exchange.

Blood and water flow accross the lamella in a counter current direction meaning they flow in the opposite direction to one another. This ensures a steep diffusion distance is maintained so the mazimum amount of oxygen is diffusing into the deoxygenated blood from the water.

The projections are held apart by water so out of water they stick together meaning fish cant survive

ventilation is required to maintain a continuous unidirectional flow. It begins with the fish openin uts mouth allowinf water to flow in. When the fish closes its mouth, the buccal cavity raises which increases the preassure and water is forced over the gill.

Question 15

Talk about gas exhange in insects.

Answer 15

Insects do not possess a transport system therefore oxygen needs to be transported directly to the tissues.
spiracles, small openings of the tubes allow gas in which then go through a network of tubes called trachae which are supported by strengthened rings. They divide into small tubes called tracheoles which extend through all the body tissues of insects directly, reduces diffusion pathway. There are three different ways of movement:

along diffusion gradient- conc of oxygen at end of tracheoles falls creating diffusion distance

mass transport- contracting muscles

water- ends are filled with water, decreases volume of tracheoles and draws water in

Question 16

Talk about the mammolian gas exhange system?

Answer 16

The lungs are a pair of lobed syructures which have a large surfave area. They are surrounded by a rib cage to protect them and they are able to inflate. External and internal intercostal muscles are between the ribs which contract and lower them. The diaphram separates the lungs

Air enters though the nose, along the trachea, bronchi and bronchioles, which are structures that enable a passage of air into and out of the lungs. They are held open with rings of cartilage.

Alveoli is where gas exchange actually takes place. These are adapted:
Thin- reduces the diffusion pathway for gases
Constant blood supply- steep concentration gradient
300 million alveoli to increase surfave area

Question 17

Talk about ventilation.

Answer 17

Ventilation is the flow of air in and out of the alveoli:

INSPIRATION- The external intercostal muscles contract and the internal muscles relax. This cayses the ribs to move upwards. The diaphram contracts and flatterns. Both of these cayse the volume of the thorax to increase, lowering the preassure creating a gradient and allowing air to be forced into the lungs

EXPIRATION- The internal intercostal muscles contrat and external muscles relex which lowers the rib cage. The diaphram relaxes and raises upwards. These actions decrease the volume inside the thorax increasing preassure and forcing air out of the lungs

Question 18

Talk about the Xylem.

Answer 18

The xylem transports water and solutes from the roots to the leaves.

They are long tubes that run up the stem of plants. They are made of dead cells called vessel elements which are stacked on top of one another and have no cell walls at the end of each element creating a continuous tube for water flow. The walls are lined with a waterproof polymer called lignin which reinforces the walls to provide structural support

Question 19

What is Transpiration?

Answer 19

The process where plants absorb water through the roots which then moves up through the plant and is released into the atmosphere through pores in the leaves.

The humidity of the atmosphere is usually less than that of the air spaces next to the stomata. As a result, there is a water potential gradient between the spaces and the air allowing water to diffuse out. This water is replaced by water evaporating from the cell walls into the mesophyll cells.
Transpiration lowers the water potential of the leaves so water is replaced via osmosis to continue the movement of water up the stem.

Question 20

Talk about the movement of water in the root.

Answer 20

Water enters the plant through root hair cells and moves into the xylem located in the centre of the root. This movement occurs due to a water potential gradient. As the water potential is higher in the soil than the root hair cells due to dissolved substances in the cell sap. This is via osmosis.

Question 21

What are the two ways water moves from the root to the xylem?

Answer 21

SYMPLASTIC PATHWAY- water enters the cytoplasm through the membrame and asses from one cell to the next through the plasmodesmata.

APOPLASTIC PATHWAY- water moves through the water filled spaces between cellulose molecules in cell walls. Water doesnt pass through any plasma membrane so can carry dissolved mineral ions and salts

When water reaches a part of the root called the endodermis, it encounters a layer of suberin known as the Casparian Strip which cant be penetrated by water, therefore for the water to cross the endodermis, the water has been moving through the cell walls must enter the symplastic pathway.

Question 22

Talk about Cohesion-Tension Theory.

Answer 22

Main factor responsible for the movement of water up the xylem.
1. Water evaporates from mesophyll cells due to transpiration
2. Water molecules form hydrogen bonds between one another and hence tend to stick together. This is known as cohesion.
3. The loss of water from the leaves creates tension as hydrogen bonds also form between water molecules and the side of the vessel
4. As water evaporates from the leaf into air spaces, more molecules of water are drawn up behind it due to this cohesion forming a continuous colum of water called a transpiration flow.
5. When water is pulled up the stem, the water potential at the bottom of the plant decreases. Water can now diffuse into the roots via osmosis down the water potential gradient

Mineral ions are actively transported into root hair cells creating a negative water potential and allowing root pressure to further push water up the column.

Question 23

Talk about the role of the Phloem

Answer 23

The phloem is the tissue responsible for transporting organic substances in plants up or down a plant to where ever it’s needed in a process called Translocation

The Phloem is made of long thing structures called sieve elements connected end to end. These end walls are perforated to form sieve plates which help sap movement and are associated with companion cells

Question 24

What is the process of mass flow theory?

Answer 24

1. Sucrose is made during photosynthesis in the leaves and diffuses down a concentration gradient via facilitated diffusion into companion cells
2. Hydrogen ions are actively transported from companion cells into spaces in the cell walls using ATP
3. Sucrose ions are transported with the hydrogen ions via co-transport into sieve tubes
4. in the Phloem, sucrose is transported along with hydrogen ions. The transport into sieve tubes causes them to have a lower water potential.
5. Due to the fact the Xylem has a higher water potential, water moves in via osmosis creating a much higher hydrostatic pressure within them
6. At the Sink cells, sucrose is actively transported into companion cells lowering sieve cells water potential allowing water to move into sink cells and the hydrostatic presssure of sieve cells lowering.
7. This means there is a high hydrostatic pressure at the source and low at the sink causing mass flow of sucrose solution in the sieve tubes

Question 25

Talk about how we investigate mass flow theory.

Answer 25

Ringing Experiments- This is when the bark and phloem of a tree is removed leaving only the xylem. Overtime, the tissues above the missing ring swell with sucrose solution and the tissue below does. This shows sucrose is transported in the phloem as the sucrose has no way of moving down

Tracer Experiments- Radioactive isotopes are used to track the movement of substances in plants. 14CO2 is incorporated into sugars. Autoradiography is used to track movement using x rays of plant stems. Where blackened areas are shown, is where 14CO2 is. These regions correspond to the area where the phloem is suggesting that’s where sugar is transported.

Question 26

What is a double circulatory system?

Answer 26

deoxygenated blood gets pumped to the lungs to be oxygenated and then back to the heart to be pumped to the rest of the body.

Question 27

Talk about the structure of the heart.

Answer 27

The structure of the heart is made of two pumps each with two chambers each (an atrium and a ventricle). The two separate pumps are needed in order to maintain a blood pressure around he whole body.

Between the atria and ventricles, there are valves which stop the back flow of blood when it contracts. These are called the left atrioventricular (bicuspid snd tricupsid) valves.

There are many blood vessels:

Aorta- connected to the left ventricle and carries deoxygenated blood to all parts of the body except the lungs

Pulmonary artery- connected to the right ventricle and carries deoxygenated blood lungs to be oxygenated

Pulmonary Vein- connected to the left atrium and oxygenated blood back from the lungs

Vena Cava- connected to the right atrium and brings deoxygenated blood back from the tissues.

Conorary Arteries- Branch off the aorta to supply the hear with blood. Blocage of these can lead to myocardial infraction or hear attack as part of the heart muscle is deprived of blood and therefore oxygen so die.

Question 28

What is the cardiac cycle and the process of it?

Answer 28

The heart undergos a series of events that is repeated in humans around 70 times each minuite. There are two phases:

Diastole- Atria and ventricles relax, elastic recoil of the heart lowers the preassure inside the heart chambers and blood returns to the heart from the vena cava and the pulmonary vein and fill the atria. Preassure then is increased in the atria util the atrioventricular valves open and blood can fow in.

Atria Systole- The atria then contract forcing any remaining blood into ventricles

Ventricular Systole- Contraction of the ventricles cause the atrioventricular valves to colse and semi-lunar valves to open thus allowing blood to leave the left ventricle through the pulmonary artery.

Question 29

What is cardiac Output?

Answer 29

Volume of blood pumped by one ventricle of the heart in one minuite usually measured in dm3 min-1.

= heart rate x stroke volume

Question 30

What is an artery and adaptations of one?

Answer 30

carry blood away from the heart into arterioles.

Muscle layer and elastic layer makes the overall thickness of the wall thoch compared to veins. This means smaller arteries can be constricted and dilated to control the volume of blood and maintain a high blood preassure and resist it from bursting under preassure. It also has no valves as blood is pumped at such a high preassure

Question 31

What are veins and adaptations?

Answer 31

Carry blood from capillaries back into the heart.
Thin muscle kayers and elastic layers as they dont need to resist preassure as its low. Thus the overall preassure of the veins is low so thickness is thinner. This also allows them to be flatterened. They also contain valves to prevent backflow.

Question 32

What are capillaries and their adaptations?

Answer 32

Tiny vessles that link arterioles into veins
Mostly the lining layer which makes them extremely thin to allow rapid diffusion of materials. They are also highly branched providing a large surface area to volume ratio for diffusion. They have a narrow lumen which pushes red blood cells to the walls reducing diffusion distance.

Question 33

What are arterioles?

Answer 33

Smaller arteries that control blood flow into capillaries

Question 34

What is tissue fluid?

Answer 34

Tissue fluid is a water liquid containing dissolved oxygen and nutrients which supply the tissues with essential solutes for exchange and take away waste products.

Question 35

How is tissue fluid made?

Answer 35

It is created when hydrostatic preassure is created by blood pumping accross the arteries into arterioles and then capillaries. This preassure forces blood fluid out of the capillaries. The only substances which are small enough to escape though the capillaries are components of tissue fluid.

The fluid is also acted upon by hydrostatic preassure which pushes some of the fluid back into the capillaries

As both the tissue fluid and blood contain solutes, they have a negative water
potential. Although the water potential of the tissue fluid is negative, it is less negative in
comparison to the blood (the blood contains more solutes). Therefore, the tissue fluid is
positive in comparison to the blood. This causes water to move down the water potential
gradient from the tissue fluid to the blood by osmosis.

The remaining tissue fluid which is not pushed back into the capillaries is carried back via the
lymphatic system.

Question 36

Define Atheromas.

Answer 36

Deposition of materials in the walls of the arteries causing a blockage. It can cause a number of cardiovascular diseases.

Question 37

What is Conorary Heart Disease.

Answer 37

The endothelium of arteriescan become damaged by the deposition of WBC’s and Fatty Materials forming hard plaque. This narrows the lumen restricting blood flow and increasing blood pressure. This can limit the amount of oxygen supply to the heart leading to a heart attack.

Risk Factors- Smoking, High Blood Preassure, High Cholestreol, Diabetes, Overweight.
Treatment- lifestyle changing, medication (statins), sugery to insert stents to widen arteries
Symptoms- Chest paim, shortness of breath, feeling faint

Question 38

What is an Aneurysm?

Answer 38

Increased blood preassure from atheromas can cause elastic fibres in the artery wall to swell in ballon-like-structure.

Question 39

What is haemoglobin?

Answer 39

Haemoglobin is a quaternary, globular protein found in the red blood cells made of two beta polypeptide chains and two alpha helices. Each molecule forms a complex containing a haem group containing an iron ion which gives it its colour and allows oxygen to bind to the heam group forming oxyharmoglobin. Each molecule can carry four oxygens.

Question 40

Talk about Oxygen Affinity and Partial Preassure.

Answer 40

Oxygen Affinity- How easily a substance binds to and releases oxygen
This is reliant on the partial preassure of oxygen. For example in the lungs, the partial preassure is high so can bind to oxygen
When partial preassure is high, oxygen loads (assosiates) readily with the haem group as it has high oxygen affinity
When the partial preassure of oxygen is low, it unloads (dissososiates) readily as it has a low oxygen affinity.

As each oxygen binds to a haem molecule, it makes the next one easier to bind due to the change of the quaternary shape.

Question 41

What is the Bohr Effect?

Answer 41

The higher the rate of respiration, the more CO2 the tissues produce lowering PH. This means that the haemoglobin shape changes more often and oxygen is unloaded more readily. In turn, the greater the haemoglobin shape change, the more oxygen available for respiration.

Question 42

Talk about the types of Haemoglobin.

Answer 42

Different organisms live in different environments with some in environments where oxygen levels are low. These organisms have different types of haemoglobin with a higher affinity of oxygen at lower partial preassyres so that even low concentrations, oxygen can be fully saturated providing them with sufficient oxygen for respiration.