exchange of substances Flashcards
the greater the size of an organism, the - - - - - - - the SA:vol ratio
smaller
why do larger organisms require specialised exchange surfaces and transport mechanisms?
to meet their metabolic requirements.
- organisms with a higher metabolic rate require more nutrients and produce more waste, therefore require a specialised exchange surface
Adaptations of gas exchange surfaces, shown by gas exchange:
- across the body surface of a single-celled organism
Single-celled organisms can exchange gases and other substances using their cell membrane.
- The rate of gas exchange is increased by a larger surface area to volume ratio.
- Single-celled organisms can be adapted to increase their surface area to volume ratio (e.g. by making themselves wide, flat or with multiple folds).
Adaptations of gas exchange surfaces, shown by gas exchange: in the tracheal system of an insect (tracheae, tracheoles and spiracles)
Insects have a tracheal system for gas exchange.
- Air enters the insect through pores in their outer surface called spiracles.
- Air then moves down the trachea, which branches off into a large number of tracheoles.
-The walls of the tracheoles are thin and porous, speeding up diffusion of gases to cells.
-Rhythmic abdominal movements push air into and out of the spiracles and maintain a steep concentration gradient
Adaptations of gas exchange surfaces, shown by gas exchange: by the leaves of dicotyledonous plants (mesophyll and stomata).
Gas exchange in plants happens through the stomata, the holes found in the lower and upper epidermis.
- Guard cells control the opening and closing of the stomata to prevent excess transpiration.
- Air spaces in the spongy mesophyll layer allow gases to circulate. Oxygen and carbon dioxide diffuse from these air spaces into the plant cells.
how do insects minimise water loss?
Insects minimise water loss by:
- Closing their spiracles if they become dehydrated
- Spiracles are surrounded by small hairs to trap water vapour and reduce the water potential gradient
- Covered by a waterproof, waxy cuticle
how to plants minimise water loss?
Plants minimise water loss by closing their stomata at night. Water moves out of the guard cells by osmosis, making the guard cells flaccid and closing the stomatal pore.
what are xerophytes?
Plants that are adapted to living in hot, dry conditions are called xerophytes.
how do xerophytes minimise water loss?
- Sunken stomata – stomata are sunken in pits which trap water vapour and reduce the water potential gradient between the inside and outside of the leaf
- Hairs around stomata – hairs trap water vapour and reduce the water potential gradient
- Curled leaves – also traps water vapour to reduce the gradient
- Fewer stomata – so less sites for loss of water
- Thicker cuticle – acts as a barrier to evaporation
how does air get to the alveoli?
When we breathe, air enters our bodies through our nose and mouth and makes its way down the trachea.
The trachea branches into two smaller tubes, called bronchi, which send air to each lung.
The bronchi divide into even smaller tubes called bronchioles which finally send the air into air-sacs called alveoli.
how does oxygen move to the bloodstream from the alveoli?
Oxygen diffuses from a region of high concentration in the alveoli to a region of low concentration in the bloodstream, where it travels to different tissues of the body and is used for respiration.
how does carbon dioxide move from the bloodstream to being breathed out?
Carbon dioxide travels in the other direction, from a region of high concentration in the bloodstream to a region of low concentration in the alveoli, where it travels up the trachea and is breathed out.
The essential features of the alveolar epithelium as a surface over which gas exchange takes place…
Adaptations of the alveoli:
- Large surface area - many alveoli are present in the lungs with a shape that further increases surface area.
- Thin walls - alveolar walls are one cell thick providing gases with a short diffusion distance.
- Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface.
- Permeable walls - allow gases to pass through.
- Good blood supply (many capillaries) - ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs.
- A large diffusion gradient - breathing ensures that the oxygen concentration in the alveoli is higher than in the capillaries so oxygen moves from the alveoli to the blood. Carbon dioxide diffuses in the opposite direction.
process of breathing in?
1) The external intercostal muscles contracts. The diaphragm contracts and moves downwards.
2) The external intercostal muscles move the ribcage upwards and outwards.
The diaphragm moves downwards. The volume of the thoracic cavity increases.
3) The increasing volume in the thoracic cavity causes the pressure in the lungs to decrease.
A pressure gradient between outside the lungs and inside the lungs is created
4) Air flows inside the lungs down the pressure gradient.
Air flows down the trachea and into the alveoli.
process of breathing out?
1) The external intercostal muscles relax. The internal intercostal muscles also contract. The diaphragm relaxes and moves upwards.
2) The internal intercostal muscles move the ribcage downwards and inwards.
The diaphragm moves upwards. The volume of the thoracic cavity decreases.
3) The decreasing volume in the thoracic cavity causes the pressure in the lungs to increase. A pressure gradient between outside the lungs and inside the lungs is created.
4) Air flows out from the lungs down the pressure gradient.
Air flows out of the alveoli and up the trachea.
what happens during digestion?
large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes.
digestion of starch…
enzyme: amylase
products: maltose
digestion of maltose, sucrose, lactose…
maltose
enzyme:maltase
products: alpha glucose molecules
sucrose
enzyme: sucrase
products: glucose and fructose
lactose
enzyme: lactase
products: glucose and galactose
