2.2 living processes in unicellular organisms

unicellular organisms are…

• organisms that consist of only one cell

• a complete unit of life still able to carry out all living processes, such as movement, reproduction, nutrition, respiration, growth, excretion and respond to stimuli.

name some examples of unicellular organisms.

amoeba sp. and paramecium sp.

• lives in freshwater ponds and lakes

• feeds on microscopic organisms and decayed organic substances

ameoba sp. …

• no fixed shape

• simplest animal cell

amoeba sp. : movement

• moves by extending out its pseudopodium (false feet) (cytoplasmic extension of any part of amoeba sp.)

• the pseudopodium extends out and the cytoplasm slowly flows into this extension, moving the organism forward

amoeba sp. : reproduction

when conditions are suitable + plenty of food: reproduce via asexual reproduction that is binary fission through mitosis

• once an amoeba sp. has grown to a certain size, its nucleus divides itself to form two daughter nuclei

• the cytoplasm then divides itself and two daughter amoeba sp. is formed

under adverse conditions (dry conditions/ low temperature/ food shortage): amoeba sp. forms spores that will germinate when the environment improves.

amoeba sp. : nutrition

amoeba sp. feeds through phagocytosis

• amoeba sp. approaches a food particle by extending its pseudopodium, surrounds and traps the food particles before engulfing it into the cytoplasm, forming a food vacuole

• the food vacuole is combined with lysosome, and the food particles are hydrolysed by the enzyme lysozyme in the lysosomes

• food is digested and nutrients are absorbed into cytoplasm. undigested food is discharged when amoeba sp. moves.

amoeba sp. : respiration

exchange of of oxygen and carbon dioxide gases occur through the plasma membrane via simple diffusion on the surface of the cell.

• being small in size, it provides a wide surface area for diffusion of gases

amoeba sp. : growth

amoeba sp. grow by synthesising new cytoplasm

• nutrients absorbed during feeding are used to build protein and cytoplasm

• this causes an increase in the size of amoeba sp. cell and growth in the cell.

amoeba sp. : excretion

waste such as carbon dioxide and ammonia are excreted via osmoregulation

• water in the freshwater habitats of amoeba sp. diffuses into the cell via osmosis and fills the contractile vacuole.

• when the contractile vacuole expands to its maximum size, contraction occurs and water is excreted from time to time

• this regulates the water content amoeba sp. and enables it to survive in its habitat.

amoeba sp. : response to stimuli

responds to stimuli (chemicals, touch or bright lights) by moving away from the stimuli to protect itself against any injury or harm.

paramecium sp. …

• has a fixed shape like a slipper.

• has to nuclei: a micronucleus and a macronucleus which are involved in reproduction

• has two contractile vacuoles which are involved in osmoregulation to excrete water.

paramecium sp. : movement

paramecium sp. moves with the help of rhythmic cilia (rows of tiny hairs on the surface of paramecium sp.) beats

• rhythmic beating by the cilia propels the paramecium sp. to move along the water

• avoiding reaction response: when encountering an obstacle, it stops, backs up, turns 30 then moves on. this repeats until it gets past the obstacle.

paramecium sp. : nutrition

presence of cilium beat around the oral groove transfers food particles into the oral groove (which leads food to gullet)

• the food particles are engulfed into the cytoplasm, forming a food vacuole

• the food vacuole is combined with lysosomes. the food particles are hydrolysed by the enzyme lysozymes in the lysosomes

• as the food particles are being digested, cytosis occurs (the food vacuole is moved in a circular path around the cell)

• food is digested and nutrients are absorbed into the cytoplasm. undigested food is excreted through a weak spot in the membrane called anal pore.

paramecium sp. : reproduction

when conditions are suitable + plenty of food: paramecium sp. reproduce via asexual reproduction that is binary fission through mitosis

under adverse conditions (dry conditions/ low temperature/ food shortage), paramecium sp. will reproduce via sexual reproduction that is conjugation

• two individual paramecium sp. from different strains come together and exchange genetic material between the nucleis

• the paramecium cells separate and can each divide to produce four new cells (total: eight daughter cells)

paramecium sp. : respiration

exchange of oxygen and carbon dioxide gases occur through the plasma membrane via simple diffusion on the surface of the cell

paramecium sp. : growth

paramecium sp. grow by synthesising new cytoplasm

• nutrients absorbed during feeding are used to build protein and cytoplasm

• this causes an increase in the size of paramecium sp. cell and growth in the cell.

paramecium sp. : excretion

excess water is excreted by osmoregulation

• carried out by two contractile vacuoles which moves around the cell to regulate water balance in cell

• when the contractile vacuoles expands to its maximum size, contraction occurs and water is excreted from time to time

• this regulates the water content paramecium sp. and enables it to survive in its habitat.

paramecium sp. : response to stimuli

responds to stimuli (chemicals, touch or bright lights) by moving away from the stimuli to protect itself against any injury or harm.