CHAPTER 2

CELL STRUCTURE AND CELL ORGANISATION

CELL ORGANISATION•Unicellular organisms•Multicellular organisms

Unicellular organisms• Single-celled organisms capable of carrying

out the following basic life processes:– Feeding– Reproduction– Respiration– Excretion– Locomotion– Sensitivity– Growth– Osmoregulation

Example of unicellular organisms

Paramecium

habitat• Amoeba– Found in fresh water puddle, ponds, wet

soil and in animal as parasites• Paramecium– Found in fresh water especially in

decaying organic matter

General features• Amoeba– Irregular shape– Diameter about 0.1mm– Its cell membrane consist of an outer

ectoplasm and inner endoplasm• Paramecium– A slipper-like shape– Covered with fine hair called cilia

Cell structure

Locomotion• Amoeba–Move by flowing its cytoplasm forward

forming a pseudopodium that help its move forward slowly

– Pseudopodium means a “false foot”• Paramecium– Uses its hair like cilia to beats against

the water, enabling its to swim

feeding• Amoeba– Omnivore – eat algae, bacteria, plant

cell and other microscopic organisms– Engulf tiny food particles using its

pseudopodia forming a bubble-like food vacuole to contain the food

– This is called phagocytosis– Digestive enzymes are produces in the

food vacuole to digest the food particles

• Paramecium– Eat bacteria and other microscopic

organic material– The sweeping movement of cilia move

the food along the oral groove into the gullet where the vacuole form

– The food vacuole circulates around the cell while the food is being digested

– Finally, an undigested food is eliminated at the anal pore

reproduction• Amoeba– Asexually– Binary fission – take place by mitotic

division of single parent cell (in favourable condition)

– Formation of spores – when condition is dry and there is insufficient food

• Paramecium– Favourable condition – asexully (binary

fission)– Unfavourable condition – sexually

(conjugation)

sensitivity• Amoeba– No recognisable sense receptor but

sensitive to touch and changes in light, temperature and chemical

– Respond by moving toward or away form the external stimulus

• Paramecium– Cilia detect the external stimuli such as

chemicals, oxygen, carbon dioxide, light, touch, and temperature changes

– Respond by moving toward or away form the external stimulus

growth• Both use amino acids from food to

synthesis their protoplasm• Growth size is always limited• If too large, less efficiency for gases

and materials diffusion to sustain life

respiration• Exchange of gaseous occur

throughout the whole cell membrane• Oxygen and carbon dioxide diffuses

down the concentration gradient

excretion• For both organisms, waste product

such as nitrogenous waste and carbon dioxide expelled by diffusion

• Solid waste in paramecium are expelled through its anal pore

osmoregulation• Water continually move into amoeba

and paramecium by osmosis• To prevent from bursting, the

contractile vacuole collect all the excess water

• When the vacuole is full, its expel the water outside the cell

• Amoeba has one contractile vacuole while paramecium have 2.

Cell specialisation in multicellular organisms

• Due to physical limitation, the size of a cell cannot grow beyond a certain size.

• To grow, organisms must increase the number of cells

• Increase of organisms size will increase all living processes–Size – demand more food and

oxygen–Quality – need for an efficient

supply of oxygen to the cells–Complexity – such as complex

organ to replace simple organelles

Cell specialisation• Important so that cells can:–Differentiate into suitable structure

to perform specialize function–Be more efficient so that processes

can take place faster

• Specialization requires some modification of the cell structure and its internal chemistry

• The process of cell development which enable its to perform a specialize function is called differentiation

Advantage of specialization• Adaptation• Grow in size• Obtain energy from a wider variety of

food• Have complex structure such as legs,

wing and other• Have access to other environmental

resources that cannot be reached by by unicellular organisms

Five level of organisation• Cell• Tissue• Organ• System• Organism

cell

tissue

organ

system

Internal environment• Environment inside organism which

is the fluid surrounding the cells• The fluid surrounding the cells is

called tissue fluid or interstitial fluid• Tissue fluid fills the narrow spaces

between the cells–bathes the cells–Keep the cells function normally

• Cells receive all their substances (nutrient and oxygen) from the blood stream through the tissue fluid

• Tissue fluid form from the plasma of blood

Factors affecting the internal environment

• Temperature• pH value• Osmotic pressure• Glucose level

temperature• In humans, the internal invironment

is maintained at 37˚C for optimum enzyme activity.

• If the temperature rises too high, enzymes are denatured and lose their abilities to function.

• If the temperature falls too low, enzymes become inactive.

pH• The pH of human tissue fluid is 7.4• This optimal pH is slightly alkaline.• Enzymes function within a narrow

range of pH.• If the pH changes, enzymes will be

denatured and lose their ability to function.

homeostasis• Maintenance of a steady state in the

internal environment• The steady state is the optimum level

for all body function• Mechanisms– Stimulus– Receptor– Corrective mechanism (Negative

feedback)

examples• Temperature• Osmotic pressure• Glucose level• pH

temperatureBody temperature higher than 37˚C.1.Temperature receptors of skin

(integumentary system) detect high temperature and send nerve impulse to the brain (nervous system)

2.Corrective machanism: brain send nerve impulses to the following system:

• Circulatory system-arterioles in the epidermis dilate (expend) to let more blood flows to he skin and body heat loss increases.

• Integumentary system-sweat is produce more which evaporates to cools the body down. Hair erector muscle relax to let the to decrease insulation.

• Endocrine system-produce hormones to reduce the metabolic rate and decrease heat produce.

3.Nagetive feedback:brings the high temperature down and back to normal again.

Body temperature lower than 37˚C.1.Temperature receptors of skin

detect the low temperature and send nerve impulses to the brain.

2.Corrective machanism:brain send nerve impulses to the following system:

• Circulatory system-arterioles in the epidermisconstrict soless blood flows to the skin and heat loss decreases.

• Integumentary system-sweat gland less active to avoid heat

loss.-the hair eractor muscles contract so

that hair “stand up” to reduce heat loss.

-skeletal muscles contract alternately (shiver) to release more heat.

• Endocrine system-produce hormones to increase the metabolic rate and heat production.

3.Negative feedback:brings the low temperature up and back to normal again.

OSMOTIC PRESSURE• High osmotic pressure (loss of water).1.Osmoreceptors in the brain detect the

high osmotic pressure in the blood and sends this massage to the pituitary gland (endocrine system).

2.Corrective machanism:the pituitary gland secretes the ADH (antidiuretic hormone) into the bloodstream which carries it to the kidney. The ADH hormone acts on the kidney to absorb more water back to the body.

3.Negative feedback: osmotic pressure decreases and return to normal.

• Low osmotic pressure (large intake of water).

1.Osmoreceptors in the brain detect the lowosmotic pressure in the blood and sends this message to the pituitary gland.

2.Corrective machanism:the pituitary gland secretes less ADH hormone and the kidney absorb less water.

3.Nagetive feedback:osmotic pressure return to normal.

GLUCOSE LEVEL• Above normal blood glucose level.1.Receptor in the pancreas detect

high blood glucose level. This cause the pancreas to secrete more insuline (hormone) into the bloodstream.

2.Corrective machanism:when insuline reaches the liver, it causes the liver to convert excess glucose into glycogen which is then store in the liver.

3.Negative feedback:blood glucose level goes back to normal.

• Below normal blood glucose level.1.Receptor in the pancreas detect low

blood glucose level. This cause the pancreas to secrete more glucagon (hormone) into the bloodstream.

2.Corrective machanism:when glucagon reaches the liver, it causes the liver to convert excess glycogen into glucose.

3.Negative feedback:blood glucose level goes back to normal.

pH• Above or below pH 7.41.Involve the following system:• Respiratory system• Excretory system• Circulatory system2.These three system work together to

maintain optimum internal environment of pH 7.4 by monitoring the concentrations of ions and salts in the blood.