Movement of Molecules In and Out of Cells
- Created by: Fionnuala Smith
- Created on: 03-02-13 17:06
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- Movement of Molecules In and Out of Cells
- Dissolved substances
- Move by: Diffusion & active transport
- Osmosis: Diffusion of water from dilute to more concentrated solution through a partially permeable membrane
- Partially permeable membrane: allows water molecules through & stops solute molecules getting through (too large)
- Osmosis and Cells
- When concentrations in & out of a cell water moves by osmosis to balance
- Osmosis gradually dilutes more concentrated solution
- e.g. from soil - plant's root hair cells along a concentration gradient
- Active Transport
- Sometimes substances are absorbed against concentration gradient.
- Requires energy from respiration
- Allows cells to absorb ions & sugar, which pass through cell membranes from very dilute solutions
- In humans sugar's absorbed from intestine & kidney tubules
- Soft drinks & sports
drinks contain water, sugar & ions to replace:
- 1) sugar used to release energy during exercise
- 2) Water & ions lost during sweating
- 1) sugar used to release energy during exercise
- |f they aren't replaced, the ion & water balance of body is disturbed & cells don't work as efficiently
- Sometimes substances are absorbed against concentration gradient.
- Exchanging Materials
- Many organ system are specialised for exchanging materials
- Large surface area, thin (short diffusion path), efficient blood supply (animals), being ventilated (animals) for gas exchange
- The larger & more complex an organism is, the more difficult exchanging materials is
- Exchange surfaces are adapted to maximise effectiveness
- In humans: Villi increase surface area of small intestine
- In humans: Alveoli increase surface area of lungs
- Villi in the Small Intestine
- Villi line the walls
- Massive surface area for exchanging materials across
- Extensive network of blood capillaries to absorb products of digestion by diffusion & active transport
- The breathing system
- Located in upper thorax (upper part of body)
- Involves lungs
- protected by rib cage
- Thorax is divided from abdomen by muscular sheet called diaphragm
- take air in & out of body so: oxygen can diffuse into your body & CO2 can diffuse from blood into air
- Alveoli in the Lungs
- air goes through trachea to lungs
- Trachea has rings of cartilage to prevent it from collapsing
- trachea divides into 2 tubes (bronchi)
- Bronchi divides into bronchioles
- bronchioles divide until they end in air sacs
- Air sacs are called alveoli (millions of them)
- Alveoli are close to blood capillaries.
- They're effeicient at exchanging O2 & CO2 because they have: large, moist surface area & excellent blood supply
- Ventilation
- Movement of air into & out of lungs is known as ventilation
- As you inhale your rib cage moves up & diaphragm flattens (contracts)
- As you exhale, your rib cage moves in & down & diaphragm moves up (relaxes)
- Artificial aids for breathing, such as ventilators, have been developed for medical use. They improve gas exchange in body.
- Exchanging Systems in Plants
- CO2 enters & leaves by diffusion
- Water & mineral ions are absorbed by roots
- Roots & leaves are adapted to carry out the exchange of materials
- Root hairs = large surface area
- Leaves = broad, thin & flat with lots of internal air spaces = largest surface area possible
- Tiny holes called
stomata on leaves.
- During photosynthesis the stomata: let CO2 in (needed for photosynthesis)
- During photosynthesis the stomata: let oxygen out (a product of photosynthesis)
- Plants mainly lose water vapour from leaves mostly through the stomata
- Movement of water through plant = transpiration
- Evaporation is more rapid in hot, dry & windy conditions
- If plants lose water through leaves than its replaced by roots, stomata close =prevents wilting
- This means photosynthesis can't take place
- Size of stomata controlled by guard cells, which surround them
- Dissolved substances
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