Unit 3: Organisms Exchange Substances With Their Environment

Question 1

Why must organisms exchange substances

Answer 1

• their external environment is different to their internal environment
• in order to survive, transfer of substances across membranes must occur

Question 2

What do organisms exchange

Answer 2

• respiratory gases
• nutrients
• excretory product
• metabolic heat
• water

Question 3

What is surface area : volume ratio and why is it important

Answer 3

• difference between surface area of cell surface membrane and overall volume of cell
• the larger the animal, the lower SA:V
• surface must be large compared to volume for efficient gas exchange

Question 4

What is the thorax

Answer 4

• lungs are housed in the thorax, an air-tight, dome shaped chamber formed by the ribcage and intercostal muscles
• thorax lined with a pleural membrane, secreting pleural fluid, which acts as a lubricant from blood plasma, maintaining surface tension and protecting lungs from friction

Question 5

What is the diaphragm

Answer 5

• a sheet of muscle attached to the body wall at the base of the ribcage
• separates the thorax and abdomen

Question 6

Flow of air from mouth into lungs

Answer 6

• inhaled at mouth or nose, pass through the trachea, pharynx and larynx
• trachea divides into two primary bronchi, one to each lung.
• bronchi divides into secondary bronchi, the bronchial tree.
• smallest bronchi divide into bronchioles, which terminate at the alveoli.

Question 7

Trachea notes

Answer 7

• lined with cillates epithelial cells, which are hair-like cells that waft mucus to the back of the throat
• goblet cells produce mucus, which acts as a method of trapping dirt and pathogens
• trachea cells havw +-shaped cartilage disks which prevent collapsing
• smooth muscle controls diameter of the airway

Question 8

Bronchiole notes

Answer 8

• leads from bronchi and go to alveoli
• mainly smooth muscles and epithelial cells
• larger bronchioles may have cartilage to maintain structure

Question 9

Alveoli notes

Answer 9

• squamous epithelial tissue and elastic fibres
• adaptations: large SA, good blood supply, short diffusion distances

Question 10

What is tidal volume

Answer 10

• the volume of air in each breath, usually between 0.4 - 0.5dm3 for adults

Question 11

What is ventilation rate

Answer 11

• number of breaths per minute, around 15 per minute at rest

Question 12

What is forced expiratory volume

Answer 12

• the maximum volume of air that can be breathed in and out

Question 13

What is forced vital capacity

Answer 13

• the maximum volume of sir it is possible to breathe forcefully out of the lungs after a deep breath in

Question 14

What is vital capacity

Answer 14

• the maximum air we can inhale and exhale

Question 15

What is residual volume

Answer 15

• the volume of air left in the lungs after the strongest exhalation

Question 16

What is total lung capacity

Answer 16

• vital capacity + residual volume, normally 5 - 6dm3.

Question 17

What is pulmonary ventilation

Answer 17

• tidal volume x ventilation rate

Question 18

Xerophytic adaptations

Answer 18

• stomata sunk in pits, to trap water vapour
• layer of hairs to trap water around stomata
• curled leaves to protect stomata from high speed winds
• reduced stomata so less water can escape
• thicker waxy cuticle to reduce evaporation

Question 19

What are endopeptidases and examples

Answer 19

• break up large proteins into smaller polypeptides, by hydrolysing bonds in the middle
• trypsin, pepsin

Question 20

What are exopeptidases

Answer 20

• break up dipeptides or amino acids off from the end of polypeptides

Question 21

Digestion of carbohydrates

Answer 21

• amylase catalyses the breakdown of starch, which is chains of glucose
• hydrolyses glycosidic bonds to produce maltose

Question 22

Digestion of disaccharides

Answer 22

• enzymes attached to the epithelium of the ileum

Question 23

Digestion of lipids

Answer 23

• lipase enzymes catalyse breakdown of lipids into monoglycerides
• bile salts emulsify lipids into droplets
• micelles help the product of lipid digestion to be absorbed

Question 24

What does the circulatory system consist of

Answer 24

• tubes called blood vessels
• a pump, the heart, keeps blood flowing through the vessels
• valves, in the heart and veins, prevent backflow of blood

Question 25

What makes it double-circulatory

Answer 25

• blood passes through the heart twice, once as deoxygenated and once as oxygenated

Question 26

Key features of a mass transport system

Answer 26

• a transport medium to transport necessary substances
• rapid enough movement to supply body and cells with what they need
• mechanisms to ensure blood flows in one direction
• via a system of vessels and tubes

Question 27

What is myogenic contraction

Answer 27

• the heart can beat without input from the nervous system, if its cells stay alive
• muscle cells (myocytes) have a slight electrical charge across their membrane, when this charge is reversed it causes them to contract
• heartbeat is initiated in the sinoatrial node, also known as the pacemaker
• consists of contraction (systole) and relaxation (diastole)

Question 28

Three steps of heart contraction

Answer 28

1) cardiac diastole - allows heart to refill with blood
2) atrial systole - pushes blood into ventricle
3) ventricular systole - pushes blood out of heart into aorta and pulmonary arteries

Question 29

Heartbeat sounds

Answer 29

Ventricular systole - ‘lub’
Diastole - ‘dub’

Question 30

Heartbeat valves

Answer 30

Ventricular systole:
- atrioventricular valves shut, because pressure in ventricle is higher than atrium
- semi lunar valves open, as pressure in ventricles is higher than in aorta
Diastole:
- semi lunar valves shut, because pressure in ventricle drops and aorta pressure is now higher
- atrioventricular valve opens as pressure in atria begins to increase as blood flows in.

Question 31

Tissues in blood vessels

Answer 31

• elastic tissue stretches and recoils to maintain pressure
• muscle tissue contracts to reduce diameter of lumen
• endothelial tissue is smooth and reduces friction