2.1-2.5 : gas exchange and membrane transport (not definitions) unit 1

why do large multicellular organisms require specialised exchange surfaces

• small SA:V ratio

• diffusion insufficient to provide all cells with the required oxygen and nutrients, and to remove all waste products

• exchange surfaces increases ration of diffusion and shorten diffusion distance

give three properties of an efficient exchange surface

• large surface area to volume ratio

• small diffusion distance

• large concentration difference

how does diffusion distance affect the rate of diffusion

the greater the diffusion distance, the further the molecules must travel hence the slower the rate of diffusion

how does concentration gradient affect the rate of diffusion

the steeper the concentration gradient , the faster the rate of diffusion

areas with high concentrations have many more particles in a certain volume and so there is a much greater chance of each particle moving to the less concentrated area

how does surface area to volume ratio affect the rate of diffusion

the larger the surface area to vlume ration, the faster the rate of diffusion

as the size of the surface area increases, more molecules can diffuse across the surface and hence the diffusion rate increases, however, as the volume increases , there is a greater distance that molecules need to diffuse through , lowering the rate of diffusion, thuse having a large surface area and small (high SA:V) the rate of diffusion is greater

describe the trachea and its function in the mammalian gaseous exchange system

• wide tube supported by c - shaped cartilage to keep the air passage open during pressure changes

• lined by ciliated epithelium cells which move mucus, produced by goblet cells , towards the throat to be swallowed, preventing lung infections

• carrier air to the bronchi

describe the bronchi and their function in the mammalian gaseous exchange system

• like the trachea they are supported by rings of cartilage and are lined by ciliated epithelium cells and goblet cells

• however , they are narrower and there are two of them , one for each lung

• they allow the passage of air into the bronchioles

describe the bronchioles and their function in the mammalian gaseous exchange system

• narrower than the bronchi

• they do not need to be kept open the cartilage, therefore mostly have only smooth muscle and elastic fibres so that they can contract and relax easily during ventilation

• they allow the passage of air into the alveoli

describe the alveoli and their function in the mammalian gaseous exchange system

• mini air scacs, lined with epithelium cells

• site of gas exchange

• walls only one cell thick, covered with a network of capillaries, 300 million in each lung, both characteristics facilitate gas diffusion

explain the process of inspiration and the changes that occur throughout the thorax

• external intercostal muscles contract while internal relax, pulling the ribs up and out

• diaphragm contracts and flattens

• volume of the thorax increases

• air pressure outside the lungs is therefore higher than the air pressure inside, so are moves in to rebalance

explain the process of expiration and the changes that occur throughout the thorax

• external intercostal muscles relax (while internal contract), bringing the ribs down and in

• diaphragm relaxes and returns to its dome-like shape

• volume of the thorax decreases

• air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out of rebalance

describe the structure and components of a typical cell membrane

contains a phospholipid bilayer which is studded with various proteins, they also typically contain cholesterol which sits in the hydrophobic portion of the membrane to regulate fluidity, other molecules like glycoproteins and glycolipids may protrude from the membrane

state five functions of cell membranes

• they act as selectively permeable barriers

• they contain receptors used for communication

• they are the site of chemical reactions

• they allow for signal transduction

• they are used for the transport and uptake of substances

what is the fluid mosaic model

a model that describes membrane structure as a ‘sea’ of mobile phospholipids studded with various proteins

what are intrinsic proteins

proteins found within the phospholipid bilayer, includes channel and carrier proteins

outline the functions of intrinsic proteins

• structural support

• carry water soluble molecules across the phospholipid bilayer

• form ion channels to enable active transport

what are extrinsic proteins

proteins found at the edges of the phospholipid bilayer

outline the functions of intrinsic proteins

• receptors

• acts as antigens, enabling cell recognition

• help cells adhere to each other

what is meant by the term compartmentalisation in biology

compartmentalisation is the separation of areas within cells which allows for the localisation of enzymes and molecules so that separate areas can carry out specific functions

what is the glycocalyx

a glycoprotein and glycolipid coating surrounding the cell membrane of some cells

state three factors that affect the permeability of the plasma membrane

• the amount of unsaturated fatty acids

• the temperature

• the amount of cholesterol present

describe how varying temperatures affect membrane permeability

• as temperature increases , the molecules have more kinetic energy and so move around more , creating gaps in the membrane

• as the temperature increases past a certain point, the proteins in the membrane become denatured, disrupting the membrane

describe the structure of cholesterol (2)

• 4 rings

• mostly hydrophobic

describe the function of cholesterol

cholesterol regulates membrane fluidity, at high temperature, it stabilises membrane and at low temperature, it keeps the phospholipids apart which allows the membrane to remain fluid

how does the amount of unsaturated fatty acids affect membrane permeability

• unsaturation causes a bend in the fatty acid tails

• this means they cannot pack as tightly together which allows more substance to pass through the membrane so the membrane is more permeable

how do organic solvents affect membrane fluidity

organic solvents can disrupt or even dissolve the membrane, making it more fluid

what is the water potential of pure water

0 KPa

state the two types of endocytosis

• phagocytosis

• pinocytosis

what is phagocytosis

the bulk uptake of solids into the cell using energy in the form of ATP

what is pinocytosis

the bulk uptake the liquids into the cell using energy in the form of ATP

what are two difference between carrier proteins and channel proteins

• channel proteins provide a hydrophilic passage for molecules to passively diffuse through

• carrier proteins can transport substances across a membrane through conformational changes which can be either passive or active