b1.4 specialisation in animal cells

B1.4 Specialisation in animal cells

Nerve cells

• Dendrites - make connections to other nerve cells
• Axon - carries nerve impulse from one place to another
• Synapses - pass impulses between nerve cell and muscle cell in the body using special transmitter chemicals

Muscle cells

• Special proteins - slide over each other making fibres contract
• Mitochondria - transfer energy for chemical reactions as cells contract and relax
• Glycogen storage - chemical broken down and used in cellular respiration by mitochondria to transfer energy needed for fibres to contract

Sperm cells

• Long tail - helps sperm move
• Acrosome - stores digestive enzymes for breaking down egg
• Nucleus - contains the genetic info to be passed on.

Root hair cells

• Help to take up water and mineral ions more efficiently 
• Always relatively close to the xylem tissue
• Mineral ions movied into the root hair cell by active transport
• Greatly increase sureface area area available for water to move into cell
• Large permanent vacuole - speeds up osmosis from soil into cell
• Many mitochondria - transfer energy needed for active transport of mineral ions into cell. 

Photosynthetic cells

• Main concern = photosynthesis and getting as much light as possible
• Chloroplasts - contain chlorophyll that trap light needed for photosynthesis
• Continous layers - max light absorption
• Large permanent vacuole - keeps cell rigid through osmosis and with photosynthetic tissue it keeps the stem supported
• Large permanent vacuole - keeps leaf spread out to absorb light.

B1.5 Specialisation in plant cells 2

Xylem cells

• Tissue responsible for bringing water and mineral ions from the roots up to the leaves and shoots. 
• Lignin builds up in cell walls and cells die. Long hollow tubes formed to allow water and mineral ions to move easily in plant.
• Spirals and rings of lignin make them strong and able to withstand pressure of the water moving up plant. 
• Supports plant. 

Phloem cells

• Tissue responsible for carrying food made by photosynthesis around body of plant.
• Phloem cells form tubes but they do not die. Dissolved food moves up and down the tubes.
• Cell walls between cells break to form sieve plates - water carrying dissolved food can move freely up and down tubes.
• Companion cells - Mitochondria in companion cells transfer energy to make dissolved food move up and down. 

B1.6 Diffusion

Substances move in and out of cell across cell membrane via diffusion.

Diffusion is the spreading out of particles of a substance in a solution or gas from an area of high to low concentration.

Rates of diffusion are affected by:

• difference in concentrations (concentration gradient) - BIG difference means FASTER diffusion. Diffusion occurs DOWN a concentration gradient.
• temperature - INCREASE means particles move FASTER

In living organisms

Oxygen passes from lungs to red blood cells by diffusion (high to low). Oxygen passes from RBC's to body cells. 

Increasing SA of cell membrane means rate of diffusion increases.

B1.7 Osmosis

Osmosis - diffusion of water from a dilute solution to a concentrated solutionthrough a partially permeable membrane.

Dilute solution - has a high concentration of water and a low concentration of solutes. Concentrated solution - has a low concentration of water and a high concentration of solutes.

Isotonic - the concentration of solutes in the solution outside the cell is the sameas the internal concentration, the solution is isotonic to the cell.

Hypertonic - the concentration of solutes in the solution outside the cell is higherthan the internal concentration, the solution is hypertonic to the cell.

Hypotonic - the concentration of solutes in the solution outside the cell is lowerthan the internal concentration, the solution is hypotonic to the cell.

If the solution outside the cell becomes too dilute - water movies into the cell and may burst

If the solution outside the cell becomes too concentrated - water moves out of cell and so may become shrivelled.

B1.8 Osmosis in plants

Water moves into plant cells by osmosis. Water creates turgor pressure that keeps the cells rigid and firm

Plants need fluid surrounding the cell to be hypotonic to the cell, with lower concentration of solutes and a higher concentration of water than the plant cellsthemselves

If solution outside cells becomes hypertonic to cells - water will leave the cell and cell will become flaccid

Plasmolysis may occur when more water is lost. The cell membrane pulls away from cell wall . 

B1.9 Active transport

Active transport moves substances from an area of low concentration to high concentration (against a concentration gradient)

Active transport requires energy produced in cell respiration in the mitochondria

Examples

PLANTS: Nitrate ions in soil (very dilute solutions), more than plant's cells so it can be absorbed by active transport (against concentration gradient)

HUMANS: Glucose (used for cell respiration) absorbed from lower concentration in the gut into higher glucose concentration in the blood. 

B1.10 Exchanging materials

Small organisms

• Large SA:V ratio 
• Means short diffusion distances (easier for exchange)

Large organisms

• Small SA:V ratio
• Means distances become larger (harder for exchange)

Larger organisms have special surfaces where exchange of materials take place to move gases, food molecules and metabolic waste.

Effectivness of an exchange surface can be increased by:

• having a large surface area
• having a thin membrane or being thin to provide a short diffusion path
• efficient blood supply maintains a steep concentration gradient 
• being ventilated makes gas exchange more efficient 

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Xylem cells

• Tissue responsible for bringing water and mineral ions from the roots up to the leaves and shoots. 
• Lignin builds up in cell walls and cells die. Long hollow tubes formed to allow water and mineral ions to move easily in plant.
• Spirals and rings of lignin make them strong and able to withstand pressure of the water moving up plant. 
• Supports plant. 

Phloem cells

• Tissue responsible for carrying food made by photosynthesis around body of plant.
• Phloem cells form tubes but they do not die. Dissolved food moves up and down the tubes.
• Cell walls between cells break to form sieve plates - water carrying dissolved food can move freely up and down tubes.
• Companion cells - Mitochondria in companion cells transfer energy to make dissolved food move up and down. 

Substances move in and out of cell across cell membrane via diffusion.

Diffusion is the spreading out of particles of a substance in a solution or gas from an area of high to low concentration.

Rates of diffusion are affected by:

• difference in concentrations (concentration gradient) - BIG difference means FASTER diffusion. Diffusion occurs DOWN a concentration gradient.
• temperature - INCREASE means particles move FASTER

In living organisms

Oxygen passes from lungs to red blood cells by diffusion (high to low). Oxygen passes from RBC's to body cells. 

Increasing SA of cell membrane means rate of diffusion increases.

Osmosis - diffusion of water from a dilute solution to a concentrated solutionthrough a partially permeable membrane.

Dilute solution - has a high concentration of water and a low concentration of solutes. Concentrated solution - has a low concentration of water and a high concentration of solutes.

Isotonic - the concentration of solutes in the solution outside the cell is the sameas the internal concentration, the solution is isotonic to the cell.

Hypertonic - the concentration of solutes in the solution outside the cell is higherthan the internal concentration, the solution is hypertonic to the cell.

Hypotonic - the concentration of solutes in the solution outside the cell is lowerthan the internal concentration, the solution is hypotonic to the cell.

If the solution outside the cell becomes too dilute - water movies into the cell and may burst

If the solution outside the cell becomes too concentrated - water moves out of cell and so may become shrivelled.

Water moves into plant cells by osmosis. Water creates turgor pressure that keeps the cells rigid and firm

Plants need fluid surrounding the cell to be hypotonic to the cell, with lower concentration of solutes and a higher concentration of water than the plant cellsthemselves

If solution outside cells becomes hypertonic to cells - water will leave the cell and cell will become flaccid

Plasmolysis may occur when more water is lost. The cell membrane pulls away from cell wall .