B2 scaling up

what is diffusion?

particles in a gas moving around in all directions- usually from an area of higher concentration to an area of lower concentration

diffusion

net movement of particles from a region of high concentration to a region of low concentration.

• they move down a concentration gradient

• it continues until the concentration of the particles is the same everywhere- at this point the gradient is zero

is energy transferred during diffusion?

no. it is a passive process. diffusion happens because of the ordinary motion of the particles

where does diffusion occur in the body

all our cells need glusoce and oxygen for respiration. our blood transports these substances around our bodies.

• then glucose and oxygen diffuse into the cells that need them

how is waste products removed after these chemical reasctions?

excess carbon dioxide is diffused out of respiring cells

how do particles enter cells?

via diffusion. they pass through the cell membrane, from a region of high concentration to an area of low concentration

what factors affect the rate of diffusion?

there are three factors:

• distance

• concentration gradient

• surface area

distance

decrease the distance for the particles to moe- it takes less time to travel a shorter distance

• blood capillaries are only one cell thick. this increases the rate of diffusion of gases in and out of the blood stream

concentration

increase the concentration gradient. the steeper the concentration gradient, the greater the net movement of particles

• plant cells use carbon dioxide for photsynthesis. the carbon dioxide concentration inside the plant cell drops. this increases the diffusion rate of carbon dioxide into the cells

surface area

increase the surface area. this allows more space for diffusion, so more particles can move in a period of time

• the small intestine wall is highly folded, increasing the surface area that is in contact with the bloodstream. this increases the rate of diffusion of molecules produced in digestion, such as glucose and amino acids.

what is osmosis?

a special type of diffusion- the diffusion of water molecules across a selectively permeable membrane.

• it explain how water get into and out of cells

what happens when a solute is dissolved in water?

water molecules cluster around the solute molecules.

• this leaves fewer water molecules free to diffuse to other areas

water potential

the concentration of free water molecules

water potential of pure water

has the highest possible water potential as all the water molecules are free to move

what causes a lower water potential?

the more concentrated a solution becomes, the lower the water potential

the greater the difference...

the greater the rate of osmosis.

where does osmosis occur in plant cells?

• 1. the surroundings are a less concentrated solution (higher water potential) than cell contents

  • cell placed into a dilute solution. it takes up water by osmosis. the pressure increases- this is called turgor pressure. the cell becomes firm or turgid.

• 2. surroundings have the same concentration as the cell contents

  • cell placed into a solution with the same concentration as its contents. there is no net movement of water. the cell remains the same.

• 3. surroundings are a more concentrated solution (lower water potential) than cell contents

  • cell placed into a more concentrated solution. it loses water by osmosis. the turgor pressure falls. the cell becomes flaccid (soft). eventually, the cell contents collapses away from the cell wall. this is called a plasmolysed cel

osmosis in animal cells

1. surroundings are a less concentrated solution (higher water potential) than cell contents

   • cell placed into a solution that is more dilute than its content. it takes up water, swells and may burst. this is called lysis

2. surroundings have the same concentration as cell contents

   • cell placed into a solution with the same water potential as its contents. there is no net movement of water. the cell remains the same.

3. surroundings are a more concentrated solution (lower water potential) than cell contents

   • cell placed into a more concentrated solution. it loses water by osmosis. the cell becomes cremated (crinkles)

what is active transport?

allows cells to move substances from an area of low concentration to an area of high concentration.

• as the particles are moving against their concentration gradient, energy must be transferred from an energy store.

three key features of active transport

• particles are transported against a cncentration gradient

• ATP is required- from respiration

• the process makes use of carrier proteins in the cell membrane

what do cells that carry out active transport contain lots of?

mitochondria.

• they can respire rapidly to produce large quantities of ATP. the rate at which active transport can occur will depend on the rate of respiration to produce the required ATP.

what are carrier proteins?

special proteins that span the width of the cell membrane.

• a particular molecule that the cell requires binds to a specific carrier protein.

• energy is transferred from an energy store to the protein so that it can change shape or rotate

• the carrier protein transports the molecule into the cell

how carrier proteins work

1. useful molecule binds to transport/carrier molecule

2. transport protein rotates and releases molecule inside cell (using ATP)

3. transport protein rotates back again, often using energy

when is active transport used?

used whenever a substance needs to be moved against a concentration gradient

example 1 of active transport

during digestion

• in your small intestine, carbohydrates are broken down into glucose. the glucose is actively transported into the bloodstream through the villi. the blood takes the glucose to wherever it is needed in the body

villi

tiny, finger-like projections that line the lumen of the small intestine, increasing its surface area and aiding in the absorption of nutrients into the bloodstream

example 2 of active transport

nerve cells

• a carrier protein actively pumps sodium ions out of the cell

• at the same time potassium ions are pumped back in

• the sodium potassium pump plays an important role in creating nerve impulses

example 3 of active transport (in plants)

taking in minerals from the soil

• plants need nitrate ions to make proteins for growth

• normally there is a normally a lower concentration of nitrate ions in the soil water surrounding the roots than in the plant

• the plant root hair cells use active transport to move these ions across the cell membrane and into the root cell

what can body cells do?

body cells dividing to replace worn out cells, to repair damaged tissue, and enable the organism to increase in size

what is mitosis?

the process by which body cells divide. each cell divides to produce two daughter cells- identical/clones of their parents.

• mitosis increases the number of cells in a multicellular

cell cycle

process of cell growth and division

1. growth of the daughter cell (interphase)

2. DNA replication (interphase)

3. movement of chromosomes

4. cytokinesis

what does the first stage of the cell cycle involve?

a cell copying its chromosomes

• this means that each new cell produced will include a complete set of genetic material. each chromosome is made of one molecule of DNA.

• so in order to copy a chromosone, its DNA must be replicated

steps of DNA replication

1. DNA molecule ‘unzips’ forming two separate strands

2. the DNA bases on each strand are exposed

3. free nucleotides in the nucleus line up against each of the strands following the rule of complementary base pairing

4. this forms DNA base pairs

5. when the whole strand is complete, there are two identical molecules of DNA.

second step of cell cycle

the movement of chromosomes/mitosis

how do the chromosomes move?

1. the chromosomes line up across the centre of the cell

2. cell fibres attach to the duplicated chromosomes and pull them apart

3. one chromosome arm (chromatid) from each set is pulled to each end of the cell

4. a new nucleus forms around each group of chromosomes

last stage of cell cycle

cytokinesis

cytokinesis

the cytoplasm and cell membranes divide in a process known as cytokinesis. this results in the formation of two genetically identical daughter cells

the the stages of cell cycle

what is a multicellular organism?

an organism which consists of multiple cells

what happens during the development of a multicellular organism?

cells differentiate. this means they become specialised to perform a particular job.

what happens when a cell becomes specialised

its structure changes so that it is better adapted to perform its function.

• this makes the entire organism more efficient, as life processes are carried out more effectively

what happens when some cells become so specialised?

they can now only perform one function within the body

• for example, in the body includes nerve cells, red blood cells, fat cells

• in plants includes root cells and leaf palisade cells

how is a sperm cell specialised?

to transfer genetical material from the male to the ovum

adaptation 1 of sperm cells

flagellum- whips from side to side to propel the sperm to the e

adaptation 2 of sperm

lots of mitochondria

• respiration occurs in mitochondria and the reactions of respiration transfer energy from chemical store so that the flagellum can move

adaptation 3 of sperm cell

acrosome

• stores digestive enzymes which break down the oure layers of the ovum to allow the sperm to transfer and incorporate its genetical material

how is a fat cell specialised?

to store fat. this can be used as a store of energy, enabling an animal to survive when food is short.

• fat cells also provide animals with insulation, and are used to form a protective layer around some organs such as the heart.

• however, too much fat in humans is dangerous

adaptation of fat cells

a small layer of cytoplasm surrounding a fat reservoir

• they can expand up to 1000 times their original size as they fill with fat

how are red blood cells specialised?

to transport oxygen around the body

adaptation 1 of RBCs

biconcave discs

• pushed in on both sides to form a biconcave shape, which increases the surface area to volume ratio, speeding up the diffusion of oxygen into the cell, and oxygen out of the cell

adaptation 2 of RBCs

packed full of haemoglobins

• this protein binds to oxygen to form oxyhaemoglobin, which is red

• haemoglobin is able to bond with oxygen so lots of it makes it easier to transport oxygen

adaptation 3 of RBCs

no nucleus

• this means that there is space to contain more haemoglobin molecules

how are ciliated cells specialised?

found in our airways

• inbetween these cells are goblet cells, which produce sticky mucus. this traps dirt and bacteria. the cilia (tiny hairs) on the top of the cells sweep the mucus away from your lungs to the back to the throat. you then swallow the mucus and any bacteria present are killed in your stomach

how are palisade cells specialised?

special for carrying out photosynthesis.

• they are found near the surface of the leaf and are packed full of chloroplasts.

• they have a regular shape to allow close packing within the leaf, maximising the absorption of sunlight.

what is the function of a stem cell?

they are undifferentiated cells which divide by mitosis, forming cells which then differentiate and become specialised

• this means that stem cells can develop into any type of specialised cell and therefore form all types of tissues and organs

what are stem cells used for?

used during developement, growth, and repair

what are the two types of stem cells?

• embryonic stem cells

• adult stem cells

embryonic stem cells

found in embryos.

• they divide by mitosis to produce all the cells needed to make an organism.

• embryonic stem cells have the ability to differentiate into all cell types

adult stem cells

found in various body tissues such as the brain, bone marrow, skin and liver.

• they are able to differentiate into different types of cells, but not into as many types as embryonic stem cells

adult stem cell examples

there are blood stem cells in your bone marrow. this can differentiate into..

• RBCs

• WBCs

• Platelets

what happens to stem cells once an animal is fully grown?

many adult stem cells remain in a non-dividing state for years.

• if activated by disease or tissue injury these cells can then start to divide. this generates many cells, which can be used to repair damage

what else can adult stem cells do?

• act as a repair mechanism for the body

• for example, the whole liver can regenerate from as little of 25% of the original organs

plants meristems

unlike animals, plants continue to grow throughout their life.

• however, only particular parts of the plant grow. these parts are called meristems.

where are stem cells found in plants?

in meristems.

how do these stem cells look?

• these cells look very different to normal plant cells.

• they are are small compared to other plant cells

• they have very thin walls, small vacuoles and no chloroplasts

can differentiated plant cells divide?

no as their cell walls are thick and rigid

medically using stem cells

have the potential to treat a range of medical conditions

• most scientific research is carried out on embryonic stem cells

• embryonic stem cells are taken from a four-five day old human embryo

• these embryos are usually spare embryos that have been created during IVF treatment

disadvantage of medically using stem cells

• can cause tumours/cancers by incontrollable cell division

• the body may reject it or view them as a foreign body.

• SC transplants may weaken immune system

what is unethical about using embryonic stem cells?

the destruction of stem cells to obtain them.

what is surface area to volume ratio?

the surface area per unit volume of an object, which is calculated as a ratio

calculating

a dice → the area of one face = 4

• total surface area= 24cm²

• volume is 8cm³

• surface area to volume ratio = 3cm² : 1cm³

why is surface are to volume ratio important?

it dictates how efficiently an organism or cell can exchange materials with its environment

what does an organism need to function properly?

to exchange substances between itself and the environment

where does this exchange of substances happen?

across the cell membrane

what are the three transport processes that living organisms use for exchange?

• diffusion

• osmosis

• active transport

single-celled organisms

(like amoeba & bacteria)

• have high SA:V ratio, which allows for the exchange of substances to occur via simple diffusion to get everything they need

what does the high/large surface area allow for?

maximum absorption of nutrients (amino acids, glucose), gases (oxygen) and secretion of waste products (carbon dioxide)

what does the small volume mean?

the diffusion distance to all areas is short

humans

and other multicellular organisms have low surface area : volume ratio

• cant rely on diffusion for all our needs

• we need to rely on specialised exchange surfaces

why cant multicellular organisms rely on simple diffusion?

as diffusion over the greater distance cannot occur fast enough to meet the cells’ demands

• they have developed different adaptations to increase surface area : volume ratio at exchange surfaces

  • gas exchange system, circulatory system, urinary system, xylem and phloem.

how do mutlicellular organisms maximise the rate of diffusion of oxygen into the bloodsteam and lungs?

contains many alveoli, which increase the surface area of the lungs

how are alveoli adapted?

to ensure efficent gas exchange. if all the alveoli in your lungs were laid out, they would cover an area equivalent to half a tennis court.

what are alveoli?

tiny air sacs at the end of the terminal bronchioles (tiny branches of air tubes in the lungs)

how does gas exchange at alveolus happen?

1. ventilation moves air in and out ad helps maintain a steep diffusion gradient

2. very thin alveolus walls give short distance to make diffusion easy

3. spherical shape of the alveolus gives relatively large surface area for diffusion

4. good blood supply maintains concentration graduent for diffusion by removing oxygen and bringing lots of carbon dioxide

digestion diffusion rate adaptations

digested food molevules are absorbed into the blood from the small intestine

• to maximise the diffusion rate, the walls of the small intestine contain fingerlike villi, which increase surface area of the intestine wall.

• microscopic microvilli on the villi wincrease the surface area even further

why are transport systems needed?

once a required substance has diffused into your body, it must be transported to where it is needed

system in animals

the circulatory system is the main transport system

• the blood carries materials to where they are required.

• for example, the liver produces urea when it breaks down excess amino acids. urea is toxic so it is transported to the kidney where it is removes (urinatory system)

properties of exchange surfaces in multicellular organisms

• a large surface area to increase the rate of transport

• a barrier that is as thin as possible to separate two regions to provide a short diffusion path as possible for substances to move across

what else do animals have?

a large network of blood vessels throughout the body

• to reduce the distance of exchange of materials between cells and the bloodstream

• to move substances towards or away from exchange surfaces to maintain concentration gradients

fick’s law

rate of diffusion is proportional to (SA x conc. gradient) / diffusion distance

• if surface area or concentration gradient doubles (or diffusion distance halves) then the rate of diffusion will double

diffusion distance

• smaller the distance molecules have to travel = faster the transport occurs

• this is why blood capillaries and alveolis only are one cell thick, to ensure the rate of diffusion across them is as fast as possible

concentration gradient

greater the difference in concentration on either side of the membrane = faster movement across it will occur

• this is because on the side with the higher concentration, more random collisions against the membrane will occur

temperature

higher the temperature = the faster molecules move as they have more energy

• more collisions against the cell membrane, therefore a faster movement across them

example of transport systems in plants

• xylem tubes carry water an dmineral ions around a plant

• phloem tubes transport sugars and amino acids

organisms must take in oxygen for..

respiration

organisms must take in water for..

transport and in multiple multicellular reactions

organisms must take in dissolved food moleucles for..

releasing energy and for growth and cell repair

organisms must take in mineral ions for..

vitamins and nutrients in small amounts to help use other nutrients efficiently

why must plants take in carbon dioxide for?

photosynthesis

what must organisms remove as waste substances

urea and carbon dioxide