Organisms Exchange their Substances with their Environment Flashcards
why do organisms need to exchange substances with their environment?
cells need to take in oxygen (for aerobic respiration) and nutrients.
they also need to excrete waste products like carbon dioxide and urea.
most organisms need to stay at roughly the same temperature, so heat needs to be exchanged too.
what is the relationship between the size of animals and their surface area: volume ratio?
smaller animals have a higher surface area: volume ratio, whereas larger animals have a smaller surface area: volume ratio.
what two things affect heat exchange?
body size and body shape.
how does body size affect heat exchange?
the rate of heat loss from an organism depends on its surface area.
if an organism has a large volume, its surface area is relatively small. this makes it harder for it to lose heat from its body.
if an organism is small, its relative surface area is large, so heat is lost more easily. this means smaller organisms need a relatively high metabolic rate, in order to generate enough heat to stay warm.
how does body shape affect heat exchange?
animals with a compact shape have a small surface area relative to their volume; this minimises heat loss from their surface.
animals with a less compact shape (have sticky bits out/more gangly) have a larger surface area relative to their volume; this increases heat loss from their surface.
what behavioural and physiological adaptations do organisms have to aid exchange?
animals with a high SA: volume ratio tend to lose more water as it evaporates from their surface. some small desert mammals have kidney structure adaptations so that they produce less urine to compensate.
to support their high metabolic rates, small mammals living in cold region need to eat large amounts of high energy foods such as seeds and nuts.
smaller mammals may have thick layers of fur or hibernate when the weather gets really cold.
larger organisms living in hot regions find it hard to keep cool as their heat loss is relatively slow. elephants have developed large flat ears to increase their surface area, allowing them to lose more heat.
what two major adaptations to gas surface exchanges have?
they have a large surface area.
they are thin which provides a short diffusion pathway across the gas exchange surface.
how do single-celled organisms exchange gases across their body surface?
they absorb and release gases by diffusion through their outer surface.
they have a relatively large surface area, a thin surface and a short diffusion pathway, so there’s no need for a gas exchange system.
how does gas exchange occur in fish?
using a counter-current system.
there’s a lower conc. of oxygen in water than in air.
water, containing oxygen, enters the fish through its mouth and passes through the gills. each gill is made of lots of thin plates called gill filaments which give it a big surface area for exchange of gases.
the gill filaments are covered in lots of tiny structures called lamellae, which increase the surface area even more.
the lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion.
blood flows through the lamellae in one direction and water flows over in the opposite direction. this counter-current system maintains a large concentration gradient between the water and the blood. the conc. of oxygen in the water is higher than that in the blood, so as much oxygen as possible diffuses from water into the blood.
how does gas exchange occur in insects?
insects have microscopic air-filled pipes called tracheae which they use for gas exchange.
air moves into the tracheae through pores on the surface called spiracles.
oxygen travels down the concentration gradient towards the cells.
the tracheae branch off into smaller tracheoles which have thin permeable walls and go to individual cells. this means that oxygen diffuses directly into the respiring cells; the insect’s circulatory system doesn’t transport oxygen.
carbon dioxide from the cells move down its own concentration gradient towards the spiracles to be released into the atmosphere.
insects use rhythmic abdominal movements to move air in and out of the spiracles.
how does gas exchange occur in dicotyledonous plants?
the main gas exchange surface is the surface of the mesophyll cells in the leaf. theyr’e well adapted for their function; they have a large surface area.
the mesophyll cells are inside the leaf. gases move in and out through special pores in the epidermis called stomata.
the stomata can open to allow exchange of gases, and close if the plant is losing too much water.
guard cells control the opening and closing of stomata.
how are insects and plants able to control water loss?
insects: if they lose too much water, they close their spiracles using their muscles. they also have waterproof, waxy cuticle all over their body and tiny hairs around their spiracles, both of which reduce evaporation.
plants: a plants’ stomata are usually kept open during the day to allow gaseous exchange. water enters the guard cells, making them turgid which opens the stomatal pore. if a plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore.
what are xerophytic plant adaptations when living in warm, dry or windy habitats where water loss is a problem?
stomata sunk in pits that trap moist air, reducing the concentration gradient of water between the leaf and the air. this reduces the amount of water diffusing out of the leaf and evaporating away.
a layer of hairs on the epidermis; which again traps the moist air around the stomata.
curled leaves with the stomata inside, protecting them from wind which helps to increase the rate of diffusion and evaporation.
a reduced number of stomata, so there are fewer places for water to escape.
waxy, waterproofed cuticles on leaves and stems to reduce evaporation.
explain the human gas exchange system.
lungs are used for gas exchange in humans.
as you breathe in, air enters the trachea (windpipe).
the trachea splits into two bronchi; one bronchus leading to each lung.
each bronchus then branches off into smaller tubes called bronchioles.
the bronchioles end in small ‘air sacs’ called alveoli.
the ribcage, intercostal muscles and diaphragm all work together to move air in and out.
what is ventilation?
this consists of inspiration and expiration.
its controlled by the movements of the diaphragm, internal and external intercostal muscles and ribcage.
explain inspiration.
the external intercostal and diaphragm muscles contract.
this causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic activity (the space where the lungs are).
as the volume of the thoracic cavity increases, the lung pressure decreases to below atmospheric pressure.
air will always flow from an area of higher pressure to an area of lower pressure so air flows down the trachea and into the lungs.
inspiration is an active process and so it requires energy.
explain expiration.
the external intercostal and diaphragm muscles relax.
the ribcage moves downwards and inwards and the diagram becomes curved again.
the volume of the thoracic cavity decreases, causing air pressure to increase to above atmospheric pressure.
air is forced down the pressure gradient and out of the lungs.
normal expiration is a passive process and so it doesn’t require energy.
what are two examples of forced expiration?
blowing out candles on your birthday cake.
coughing.
explain forced expiration.
the external intercostal muscles relax and the internal intercostal muscles contract, pulling the ribcage further down and in. this movement is said to be antagonistic.
where does human gaseous exchange occur?
in the alveoli.
what are alveoli made of?
a single layer of thin, flat cells called alveolar epithelium.
explain gas exchange in the alveoli.
there is a huge number of alveoli in the lungs, which means there’s a big surface area for exchanging oxygen and carbon dioxide.
the alveoli are surrounded by a network of capillaries.
oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium (forms the capillary wall) and into haemoglobin in the blood.
carbon dioxide diffuses into the alveoli from the blood, and is breathed out.
