gas exchange

1) cells need to take in oxygen (for aerobic respiration) and nutrients 2) organisms need to excrete waste products like carbon dioxide and urea 3)most organisms need to stay roughly at the same temperature, so heat needs to be exchanged too

smaller organisms have a larger surface area: volume ratio than larger organisms

an organism needs to be able to provide each cell with glucose and oxygen for respiration and also needs to remove waste pruducts from every cell to avoid damaging itself in single celled organisms, these substances can diffuse directly in and out of the cell through the cell surface membrane due to the diffusion distance being so short however in multicellular organisms, diffusion across the membrane is too slow because some cells are deep within the body so are too far away to be diffused into from the outer environment larger organisms have a low surface area: volume ratio, so its difficult to exchange enough substances for a large volume of organism with a relatively small surface area therefore larger organisms need a specialised exchange system

the rate of heat loss depends on the SA:V ratio of an organism e.g a hippo has a small surface area relative to its volume, therefore its harder for it to lose heat compared to a mouse which has a large surface area relative to its volume, making it a lot easier for them to lose heat smaller organisms therefore need a relatively high metabolic rate in order to generate heat to maintain their temperature

animals with a compact shape have a small SA:V ratio which minimises heat loss from their bodies animals with a less compact shape have a larger surace area relative to their volume which increases heat loss from their surface whether an animal has a compact shape or not is dependent on the temperature of its environment e.g an arctic fox has small ears and a round head to reduce its SA:V ratio, reducing heat loss to maintain its temperature in its cold environment the african bat eared fox has large ears and a more pointed nose to increase its SA:V ratio, increasing rate of heat loss so it can maintain its temperature in its hot environment

animals with a high SA:V ratio tend to lose more water as it evaporates from their surface- some desert animals have kidney structure adaptations so they produce less urine to compensate to support their metabolic rates, small mamals living in cold regions need to eat larger amounts of high energy food 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 e.g elephants and hippos find it hard to lose hear, so struggle to keep cool. elephants have adapted to have large flat ears to increase their surface area to allow them to lose more heat and hippos have learnt to spend most of the day in water to help them lose heat

1) they have a large surface area 2) theyre thin (often just one layer of epithilial cells) to provide a short diffusion pathway 3)the organism also maintains a steep diffusion gradient of gases across the exchange surface

1) single celled organisms absorb and release gases by diffusion through their surface membrane 2) they have a relatively large surface area, a thin surface and a short diffusion pathway so oxygen can take part in biochemical reaction as soon as it enters the cell, so theres no need for a specialised gas exchange system

each gill is made of lots of thin plates called gill filaments which give a large surface area for gas exchange the gill filaments are covered in structures called lamellae which also increase the surface area further the lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion

theres a lower concentration of oxygen in water than in air, so fish have adaptations to increase oxygen uptake 1) water containing oxygen enters the fish through its mouth and passes out through the gills 2) blood flows through the lamellae in one direction and water flows in the opposite way to maintain a large concentration gradient between the water and blood the concentration of oxygen is always higher in the water than in the blood so maximum water uptake diffuses into the blood

1) insects have microscopic air filled pipes called trachea which they use for gas exchange 2) air moves into the trachea through pores on the surface of the insect called spiracles 3) oxygen travels down its concentration gradient towards the cells 4) the trachea branch off into smaller tracheoles which have thin, permeable walls and go to individual cells- so oxygen can diffuse directly to respiring cells as the insects circulatory system doesnt transport oxygen 5) carbon dioxide from the cells moves down its concentration gradient towards the spiracles to be released 6) insects use rhythmic abdominal movements to move air in and out of the spiracles

1) plants need carbon dioxide for photosynthesis whic produces oxygen as a waste product and need oxygen for respiration which produces CO2 as a waste product 2) the main gas exchange surface is the surface of the mesophyll cells in the leaf, which are well adapted for their function as they have a large surface area 3) the mesophyll cells are inside the leaf- gases move in and out through stomata in the epidermis 4) 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 the stomata

1) if insects are losing too much water, they close their spiracles using muscles they also have a waxy cuticle all over their body and tiny hairs around their spiracles to reduce evaporation as the diffusion gradient of water decreases 2) stomata are usually kept open all day to allow gas exchange. water enters the guard cells making them turgid to open the stomata. if the plant starts becoming dehydrates, the guard cells lose water and become flaccid, closing the pore

xerophytes are plants which are specially adapted to live is warm, dry or windy habitats where water loss is a problem

stomata sunken into pits that trap moist air, reducing the concentration gradient of water between the leaf and air- this reduces the amount of water diffusing out of the leaf and evaporating away a layer of hairs on the epidermis to trap moist air around the stomata- reducing the concentration gradient between the leaf and air curled leaves with the stomata inside, protecting them from the wind- windy conditions increase the rate of diffusion and evaporation reduced number of stomata so there are fewer places for water to escape a waterproof, waxy cuticle on leaves and stems to reduce evaporation

as you breathe in, air enters the trachea, which splits into two bronchi (one bronchus leading to each lung) each bronchus then brances off into smaller bronchioles which have alveoli on the ends of them (this is where gases are exchanged) the diaphragm, intercostal muscles and ribcage work together to move air in and out

the diaphragm and external intercostal muscles contract which raise the ribcage the chest cavity volume increases and the chest cavity pressure falls below atmospheric air moves into the lungs

the diaphragm and external intercostal muscles relax which causes the ribcage to fall chest cavity volume decreases and pressure rises above atmospheric air moves out of the lungs

contraction of the intercostal muscles isnt required for shallow breathing theyre usually only used for forced expiration- so breathing out hard or blowing

each alveolus is made from a single layer of thin, flat cells called alveolar epithelium there a huge number of alveoli in the lungs which means theres a large surface area for oxygen and carbon dioxide to be exhanged the alveoli are surrounded by a network of capillaries oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium into the haemoglobin in the blood- so oxygen diffuses directly into the surrounding capillaries, down its diffusion gradient carbon dioxide diffuses into the alveoli from the blood and is breathed out

1) they have a thin exchange surface- the alveolar epithelium is only one cell thick so there is a short diffusion pathway 2) alveoli provide a large surface area for gas exchange in the lungs, since there are so many of them 3) theres also a steep concentration gradient of oxygen and carbon dioxide between the alveoli and the capillaries which increases the rate of diffusion- this is maintained by the flow of blood and ventilation

1) tidal volume is the volume of air in each breath- usually between 0.4 and 0.5dm3 for adults 2) ventilation rate is the number of breaths per minute- for a healthy person at rest its usually around 15 breaths 3) forced expiratory volume (FEV)- the maximum volume of air that can be breathed out in 1 second 4) forced vital capacity (FVC)- the maximum volume of air that can be forcefully breathed out after a deep breath in

doctors can figure out tidal volume, ventilation rate and other measures of breathing from the graph produced from a spirometer

when someone becomes infected with the tuberculosis bacteria, the immune system builds walls around the bacteria in the lungs which forms small hard lumps called tubercules the infected tissue within the tubercules dies which damaged gas exchange surfaces, so tidal volume is decreased tuberculosis causes fibrosis which further reduces tidal volume a reduced tidal volume means less air can be inhaled, so infected people need to breathe faster to take in enough oxygen common symptoms include, persistent coughing, coughing up blood and mucus, chest pains, shortness of breath and fatigue