ASSESSMENT TOPIC 1: CELLS AND MICROORGANISMS
INVESTIGATIONS FOLIO
“How do Unicellular organisms living in water control the entry/exit of water from their cells? Are they
able to live in any environment? How may this be tested?”
Amoeba bacteria is a type of unicellular prokaryotic organism that has numerous adaptions that enable it to live in fresh water
and marine environments (Riaz 2016). There are several factors that allow amoeba to control the entry and exit of water. The
adaptations and features of amoeba cells that will be discussed include the cell membrane, osmosis, active transport, contractile
vacuoles, osmoregulation, exocytosis, and endocytosis (phagocytosis and pinocytosis).
Amoeba’s have a cell membrane which is a complex structure found after the cell wall that encloses the cytoplasm. The
membrane is referred to as being semipermeable and fluid mosaic – that is only certain molecules can go though and the
membrane proteins can move around (Halls 2018). Channel proteins are necessary to transport large molecules across the
membrane. These types of molecules can’t go through unfacilitated as the membrane is constructed out of a phospholipid
bilayer. This is a series of fatty acid chains with hydrophilic heads and hydrophobic tails. The hydrophilic heads face the
cytoplasm and have a slight positive charge which makes them attracted to water. The hydrophobic tails face the extracellular
fluid and have a slight negative charge which makes them repel water. After water has crossed the cell wall, it is transported
across the membrane through aquaporons (channel protein) located in between the phospholipids (Halls 2018). This form of
transport is called osmosis, which is the passive diffusion of water across the cell membrane along a concentration gradient
(Halls 2018).
Amoeba survive in the hypotonic state which has a higher concentration of water outside the membrane (Ernest 2015). This is
because if too much water comes into the cell, it will swell up and rupture and too little will cause the cell to dry up and die
(Halls 2018). Active transport is required for amoeba to transport water against the concentration gradient outside of the cell
using energy (ATP) (Biology Mad 2005).
Amoeba controls the amount of water inside of the cell by its contractile vacuoles which pump water and other waste products
outside of the cell in the process called osmoregulation (Battista 2018). Contractile vacuoles are a type of pump protein which
actively transport water by expanding when water enters the cell and contracting when filled, bringing the water and waste
products outside (Rader 2015). Osmoregulation controls the water content in the cell to regulate the osmotic pressure caused
by the difference in concentration of solutes between the inside and outside the cell membrane (Battista 2018). This is
necessary as without contractile vacuoles, osmosis would cause more water to come into the cell (Riaz 2016). Osmoregulation
works to remove waste products and water using exocytosis where the vacuole will fuse into the cell membrane to expel
substances (Singh 2016).
Amoeba has pseudopodia (false feat) which help it move around in water. The pseudopodia surround food and take it inside the
cell through a process of phagocytosis which is also a type of active transport and endocytosis (BBC Bitesize 2016). In
endocytosis, the cell membrane ingests various molecules. In phagocytosis, amoeba senses the presence of food due to
chemicals in the environment and moves towards the food, wrapping its cell membrane around sealing the food in a vesicle
(Rader 2015). Amoeba organisms will typically ingest bacteria, algae, plant cells and microscopic protozoa (Rader 2015).
Amoeba like any cell, absorbs extracellular fluids using pinocytosis which is a type of active transport and endocytosis. The
membrane wraps around particles and forms vesicles which the molecules inside are ingested or absorbed into the cytosol
(Rader 2015).
To test experimentally whether the concentration of water increases with amoeba in an ethical way, the amoeba could be
placed in two beakers, one with 2% sodium chloride solution (higher concentrations would kill the organism) and the other with
fresh water. The amoeba would be left in the solutions for 1o minutes then carefully removed using a spoon and placed back
into fresh water. The remaining water would then be measured. This experiment doesn’t harm any organisms and will test the
change in water volume.
Word count (excluding references): 642 words
INVESTIGATIONS FOLIO
“How do Unicellular organisms living in water control the entry/exit of water from their cells? Are they
able to live in any environment? How may this be tested?”
Amoeba bacteria is a type of unicellular prokaryotic organism that has numerous adaptions that enable it to live in fresh water
and marine environments (Riaz 2016). There are several factors that allow amoeba to control the entry and exit of water. The
adaptations and features of amoeba cells that will be discussed include the cell membrane, osmosis, active transport, contractile
vacuoles, osmoregulation, exocytosis, and endocytosis (phagocytosis and pinocytosis).
Amoeba’s have a cell membrane which is a complex structure found after the cell wall that encloses the cytoplasm. The
membrane is referred to as being semipermeable and fluid mosaic – that is only certain molecules can go though and the
membrane proteins can move around (Halls 2018). Channel proteins are necessary to transport large molecules across the
membrane. These types of molecules can’t go through unfacilitated as the membrane is constructed out of a phospholipid
bilayer. This is a series of fatty acid chains with hydrophilic heads and hydrophobic tails. The hydrophilic heads face the
cytoplasm and have a slight positive charge which makes them attracted to water. The hydrophobic tails face the extracellular
fluid and have a slight negative charge which makes them repel water. After water has crossed the cell wall, it is transported
across the membrane through aquaporons (channel protein) located in between the phospholipids (Halls 2018). This form of
transport is called osmosis, which is the passive diffusion of water across the cell membrane along a concentration gradient
(Halls 2018).
Amoeba survive in the hypotonic state which has a higher concentration of water outside the membrane (Ernest 2015). This is
because if too much water comes into the cell, it will swell up and rupture and too little will cause the cell to dry up and die
(Halls 2018). Active transport is required for amoeba to transport water against the concentration gradient outside of the cell
using energy (ATP) (Biology Mad 2005).
Amoeba controls the amount of water inside of the cell by its contractile vacuoles which pump water and other waste products
outside of the cell in the process called osmoregulation (Battista 2018). Contractile vacuoles are a type of pump protein which
actively transport water by expanding when water enters the cell and contracting when filled, bringing the water and waste
products outside (Rader 2015). Osmoregulation controls the water content in the cell to regulate the osmotic pressure caused
by the difference in concentration of solutes between the inside and outside the cell membrane (Battista 2018). This is
necessary as without contractile vacuoles, osmosis would cause more water to come into the cell (Riaz 2016). Osmoregulation
works to remove waste products and water using exocytosis where the vacuole will fuse into the cell membrane to expel
substances (Singh 2016).
Amoeba has pseudopodia (false feat) which help it move around in water. The pseudopodia surround food and take it inside the
cell through a process of phagocytosis which is also a type of active transport and endocytosis (BBC Bitesize 2016). In
endocytosis, the cell membrane ingests various molecules. In phagocytosis, amoeba senses the presence of food due to
chemicals in the environment and moves towards the food, wrapping its cell membrane around sealing the food in a vesicle
(Rader 2015). Amoeba organisms will typically ingest bacteria, algae, plant cells and microscopic protozoa (Rader 2015).
Amoeba like any cell, absorbs extracellular fluids using pinocytosis which is a type of active transport and endocytosis. The
membrane wraps around particles and forms vesicles which the molecules inside are ingested or absorbed into the cytosol
(Rader 2015).
To test experimentally whether the concentration of water increases with amoeba in an ethical way, the amoeba could be
placed in two beakers, one with 2% sodium chloride solution (higher concentrations would kill the organism) and the other with
fresh water. The amoeba would be left in the solutions for 1o minutes then carefully removed using a spoon and placed back
into fresh water. The remaining water would then be measured. This experiment doesn’t harm any organisms and will test the
change in water volume.
Word count (excluding references): 642 words
