Exchange

Question 1

What is plasma?

What are platelets?

Answer 1

plasma: the watery part of the blood where cells are transported .

Contains dissolved glucose, amino acid, urea, co2 and proteins . Also distributes heat

platelets = clot at the site of wound

Question 2

What is the purpose of a mass transport system and why do multicellular organisms need one?

Answer 2

maintains the diffusion gradients that bring materials to and from the cell surface membrane

Multicellular organisms need one because:

• the majority of cells are too far from exchange surfaces (outside environment) for diffusion alone to supply or remove their tissue fluid with the various materials needed to keep its composition relatively constant = it would be too slow for it to be by diffusion alone
• larger animals have a low surface area to volume ratio = difficult to exchange enough substances to supply a large volume of an animal through a relatively small outer surface

Question 3

How does a flattened shape help with exchange

Answer 3

no cell is ever far from the surface

Question 4

Describe how having a compact shape or a less compact shape is an adaptation for exchange

Answer 4

more compact = small SA: V = minimises heat loss

less compact = large SA:V = increases heat loss

Question 5

Why do animals with a large surface area to volume ratio have a higher rate of respiration?

Answer 5

to maintain body heat as large SA : V means lots of heat is lost

Question 6

Describe how gas exchange happens in a single-celled organism

Answer 6

due to being small, these organisms have a large SA: V. Oxygen is absorbed by diffusonacross their body surface, which is only covered by a cell-surface membrane.

CO2 from respiration diffuses out across their body surface

Question 7

Describe the Tracheal system in insects

Answer 7

Trachea = supported by strengthened rings to prevent them from collapsing

Trachea divide into smaller dead-end tubes = tracheoles

tracheoles extend throughout all the body tissues of the insect = oxygen brought directly to respiring tissues = short diffusion pathway fro the tracheole to any body cell

Question 8

What is ventilation?

Answer 8

breathing (air being moved constantly in and out of the lungs)

Question 9

What happens during inspiration? (Diaphragm, intercoastal muscles, ribs, volume of thorax, pressure of the thorax compared to the outside)

Answer 9

Diaphragm muscles contract, causing it to flatten. External intercostal muscles = contract causing the Ribs to move upwards and outwards, which increases the volume of the thorax

the volume of thorax= increases causing a reduction in the pressure of the lungs,

pressure of the thorax compared to the outside= less than outside,so air is forced into the lungs

Question 10

What happens during expiration? (Diaphragm, intercoastal muscles, ribs, volume of thorax, pressure of the thorax compared to the outside)

Answer 10

Diaphragm muscles relax and domes up.

External intercostal muscles = relax decreasing volume of the thorax causing the ribs to move downwards and inwards, which decreases the volume of the thorax.

due to having elastic tissue, the lung recoils

intercoastal muscles = contract

the volume of thorax= decreases causing an increase in the pressure of the lungs,

the pressure of the thorax compared to the outside= more than outside,so air is forced out of the lungs

Question 11

What is the main cause of air being forced out

Answer 11

the recoil of the elastic tissue in the lungs

Question 12

Why do mammals need large volumes of oxygen to be absorbed and large volumes of co2 to be removed?

Answer 12

• they are relatively large organisms with a large volume of living cells
• they maintain a high body temperature which is related to them having high metabolic and respiratory rates

Question 13

What are lungs?

Answer 13

a pair of lobed strucutres made up of a series of highly branched tubules (bronchioles) , which end up in tiny air sacs (alveoli)

Question 14

Describe the structure and adaptations of the trachea

Answer 14

flexible airway supported by rings of cartilage, which prevents the trachea collapsing as the air pressure inside falls when breathing in

tracheal walls are made up muscle lined with ciliated epithelium and globet cells = produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards the throat

cartilage is c-shaped to give flexibility

Question 15

What is the bronchi and describe the structure and adaptation of the bronchi

Answer 15

two divisions of the trachea

produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards the throat

supported by cartilage= prevents collapsing as the air pressure inside falls when breathing in

Question 16

What is the bronchicles and describe the structure and adaptation of the bronchicles

Answer 16

series of branching subdivisions of the bronchi

walls are made of muscle lined with epithelial cells

muscle allows them to constrict so that they can control the flow of air in and out of the alveoli

Question 17

What is the alveoli and describe the structure and adaptation of the alveoli (3 adaptations)

Answer 17

small air sacs at the end of the bronchioles

between alveoli there are some collagen (prevent collapsing) and elastic fibres= allow alveoli to stretch as they gill with air when breathing in

the alveoli are lined with epithelium

alveoli spring back during breathing out in order to expel the carbon dioxide-rich air

Question 18

What the adaptations of the alveoli for gas exchange

Answer 18

• Red blood cells are slowed as they pass through pulmonary capillaries allowing more time for diffusion
• the distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
• the walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion tails place is very short
• alveoli and pulmonary capillaries have a very large total surface area
• breathing movements constantly ventilate the lungs and the action of the heart constantly circulates the blood around the alveoli. together these ensure that a steep concentration gradient of gases to be exchanged is maintained
• blood flow through the pulmonary capillaries maintains a concentration gradient

Question 19

Describe how ventilation helps to maintain the difference in oxygen concentration between the alveoli and the lung capillaries

Answer 19

Ventilation removes the remaining gas in the alveoli, which has a low concentration of oxygen and a comparatively high concentration of carbon dioxide, and replaces it with fresh atmospheric air, with a high concentration of oxygen and low carbon dioxide.

Question 20

Describe and explain how the structure of the mammalian breathing system enables efficient uptake of oxygen into the blood ( 6 marks)

Answer 20

• alveoli provide a large surface area
• walls of alveoli thin to provide a short diffusion pathway
• walls of capillary thin/ close to alveoli provides a short diffusion pathway
• walls of capillaries alveoli have flattened cells
• cell membrane permeable to gases
• many blood capillaries to provide a large surface area
• Ventilation maintains a diffusion gradient
• wide trachea
• bronichioles allow efficient flow of air
• cartilage rings keeps airways open

Question 21

What are the adaptions of the leaf for gas exchange?

Answer 21

• many stomata and no cell is far from a stoma and therefore the diffusion pathway is short
• numerous interconnecting air spaces that occur throughout the mesophyll, so that gases can readily come in contact with mesophyll cells
• the large surface area of mesophyll cells for rapid diffusion.

Question 22

What is the definition of digestion?

Answer 22

The hydrolysis of large biological products to small biological molecules with the use of enzymes

Question 23

What is the definition of absorption?

Answer 23

The movement of the molecules from the lumen of the ileum, through the ieum lining into the bloodstream

Question 24

How is food, in general, digested?

Answer 24

• Buccal cavity = mechanical digestion and mastication (chewing) takes place.
• Saliva in the mouth consists of mucin (binds food together), salivary amylase (digests starch to maltose) and mineral salts (regulates pH around 7, neutral).
• Peristalsis of the circular muscle contracts and relaxes to push food down.
• It usually takes between 4 and 8 seconds for food to travel from mouth to stomach.
• stomach = Mechanical digestion takes place here (churning of the stomach makes food break down in size giving it a larger surface area). While food is in the stomach it mixes with gastric juice by churning. Food in the stomach stimulates stomach wall to produce gastrin (transported in the blood).
• Early small intestine = input of panreatic juices
• muscles in the intestine wall push the food along the ileum
• The large intestine absorbs water (by osmosis), minerals and vitamins.
• Faeces are stored in the rectum and then egested through the sphincter muscle called the anus.

Question 25

How are carbohydrates digested?

Answer 25

Saliva enters mouth from salivary glands. Salivary amylase produced in the mouth hydrolyse the glycosidic bonds in starch = maltose. This also contains mineral salts that help to maintain the pH at around neutral (optimal pH for amylase)

enters stomach and the acid denature the amylase and prevents further hydrolysis of the starch

food passed into small intestine, mixes with pancreatic juice, which has pancreatic amylase, continues the hydrolysis of remaining starch to maltose. Alkaline salts are produced by pancreas and intestinal wall to maintain the pH at around neutral so that amylase can function.

epithelial lining in intestine wall produces membrane- bound disaccharidase (maltase), which hydrolyses the maltose from starch breakdown into alpha glucose

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Question 26

What are membrane bound disaccharidases?

Answer 26

maltase that are not released into the lumen of the ileum but is part of the cell-surface membrane of the epithelial cells that line the ileum

Question 27

How are lipids digested?

Answer 27

They begin digestion in the small intestine

bile salts produced in the liver, stored in the gall bladder, are secreted into the small intestine and emulsify lipids into micelles (tiny droplets) to increase SA of lipids= greater access for lipases

lipases produced in the pancreas are secreted into the small intestine. This hydrolyses the ester bond found in triglycerides to form fatty acids and monoglycerides.

Question 28

Why is emulsification useful?

Answer 28

because it increases the surface area of the lipids so that the action of lipases is speeded up

Question 29

How are proteins digested?

Answer 29

Begin digestion in the stomach by endopeptides (hydrolyse peptide bonds in the middle of polypeptides) and break down the polypeptides into smaller peptide bonds

HCL in the stomach maintains the optimum pH for these enzymes

In the ileum of the small intestine where exopeptides released from the pancreas (hydrolyse the peptide bonds found at the ends of polypeptides) = many dipeptides

membrane-bound dipeptidases will hydrolyse the peptide bonds within the dipeptides = amino acids