Chemistry: Diffusion, Osmosis, Active transport, Exchange surface

Diffusion

The net movement of particles from an area of higher concentration to an area of lower concentration (down concentration gradient) until equilibrium. Passive , happen in gas and liquid.

Factors affecting diffusion (to increase rate)

Steeper the concentration gradient, higher temperature, larger surface area, and thinner membrane (less distance).

Concentration gradient

The difference in concentration between two areas; a steeper gradient results in a faster rate of diffusion.

Net movement

If there’s overall more particles/molecules on one side

Examples of diffusion in animal cells

Alveoli in lungs: oxygen diffuse from alveoli to blood. Carbon dioxide diffuse from blood to alveoli to be exhaled

Villi in small intestine: digested food molecules-glucose/amino acid diffuse into bloodstream

Examples of diffusion in plant cells

Leaf, somata: Carbon dioxide diffuse in and oxygen and water vapour out through stomata

Diffusion in plasma membrane

Plasma membrane control what enter and leave the cell and surround it.

It’s partially permeable

Only small molecules can fit through: water, glucose, amino acid, oxygen. Big molecules: protein, starch can’t.

Large SA:V ratio

Single celled organisms: (small organisms- amoeba) have large SA:V so large surface area of cell membrane means more particles to diffuse at once so increase rate of diffusion. (Rely on diffusion only)

Small SA:V ratio

Multicellular organism: (big organisms-human) have small SA:V so volume increases faster then surface area so as cell gets bigger, SA:V decreases so less diffusion. (Diffusion distance is too large to meet demands of cells and organisms) (Rely on active transport: blood vessels, xylem. And exchange surface: alveoli, root hair cells)

Osmosis

The net movement of water molecules across partially permeable membrane from high to low concentration until equilibrium (down concentration gradient) (passive)

Partially permeable membrane

A membrane that allows certain small dissolved molecules to pass through: water, glucose , amino acid while blocking larger molecules: starch, protein

Animals and plants in hypotonic solution

low solute

Animal:burst (lysis)

Plant:normal (turgid)

Animal and plants cells in isotonic solution

Solute=solvent

Animal: normal

Plant: limp (flaccid)

Animals and plant cells in hypertonic solution

High solute

Animal: shrivel (cremated)

Plant: cytoplasm shrink (plasmolysed)

Independent

Thing you change

Dependent

Thing you measure

Control

Thing you keep the same

Active transport

The net movement of particles across a cell membrane from low to high concentration (dilute to concentrated solution) (against their concentration gradient) requiring energy from respiration released by mitochondria .

Examples of active transport in plants

Absorption of mineral ions (magnesium) by root hair cell for chlorophyll. Active transport move ions into cell then up to xylem to leave. Many mitochondria for energy and large surface area from root hair protruding out to oil.

Example of active transport in animals

Lumen in small intestine: digested food like sugar is dissolved into glucose in lumen.Active transport move glucose to cell then blood the around body. Many mitochondria for energy.

Exchange surfaces

A specialised area of multicellular organism, adapted to maximise the exchange of materials like gases or dissolved substances with environment. Increases the SA:V ratio

Characteristics of efficient exchange surfaces in lungs

Large surface area

Number of alveoli

Reduce diffusion distance: thin membrane(one cell thick) and close proximity between capillaries & alveolus

Steep concentration gradient: good blood supply and ventilation

What diffuse into cells

Oxygen

Glucose

Water

Mineral/ions

What diffuse out of cells

Carbon dioxide

Urea

Oxygen

Potato osmotic practical

If potato loose mass, water have osmose out of cell through partially permeable membrane because solution in cell is less concentrated then surrounding.

If potato gain mass, water have osmose into cell because solution in surrounding is more dilute then cell.

Percentage change in mass

Final mass - initial mass / initial mass x100

Graph interpretation in osmosis experiment

X axis= concentration of salt solution (mol/dm3)

Y axis= mean % change in mass

Chloroplast

Photosynthesis to produce glucose/sugar

Mitochondria

Aerobic respiration to release energy

Why are nitrate ions transported by active transport not diffusion

Nitrate ions are more concentrated in cells then soil so can not simply rely on mineral ions moving into cell by diffusion. It needs to go against concentration gradient and require energy.

What happens to movement of molecules once equilibrium is reached

Evenly distributed, no net movement