U NIT 1: O RGANISMS AND L IFE P ROCESSES
All living organisms are composed of units called cells. Organisms which contains different types of cells are celled multi-cellular.
Characteristics shared by living organisms
Require nutrition plants make their own food; animals eat other organisms
Respire release energy from their food
Excrete get rid of waste products
Respond to stimuli are sensitive to changes in their surroundings
Move by the actions of muscles in animals, and slow growth movements in plants
Control their internal conditions maintain a steady state inside the body
Reproduce produce offspring
Grow and develop increase in size and complexity using materials from their food
Organelles – any of the specialized structures within a cell that perform a specific function (e.g., mitochondria, ribosomes, endoplasmic
reticulum). Organelles in unicellular organisms are the equivalent of organs in multicellular organisms.
Cells – the basic structural, functional, and biological unit of all known organisms. A cell is the smallest unit of life. Cells are often called the
"building blocks of life".
Tissues- a cellular organisational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular
matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of
multiple tissues.
Organs - a group of tissues in a living organism that have been adapted to perform a specific function.
Systems - a group of body organs or structures that together perform one or more vital functions — circulatory system, digestive system,
endocrine system, limbic system, nervous system, reproductive system, respiratory system.
Cell structures and functions
The living material that makes up a cell is called cytoplasm sloppy jelly
– complex material made of different structures which are called
organelles.
The largest organelle in the cell is the nucleus.
Nearly all cells have a nucleus. The few types
which don’t have are usually dead (e.g. the
xylem vessels) or don’t live for very long (e.g.
red blood cells).
Nucleus controls the activities inside the cell. –
contains chromosomes (e.g. in human cells) which carries the genetic material. Genes control the activities in the
cell by determining which proteins the cell can make. The DNA remains in the nucleus, the instructions for
making proteins are carried out of the nucleus to the cytoplasm, where the proteins are assembled on
ribosomes.
One very important group of proteins found in cells are enzymes. Enzymes control the chemical reactions that
take place in the cytoplasm.
All cells are surrounded by a cell membrane. thin layer – forms a boundary between the cytoplasm of the cell
and the outside. partially permeable – small molecules can pass through. When the membrane can control
the movement of some substances selectively permeable.
One organelle that is found in the cytoplasm of all living cells is the mitochondrion. carry out some of the
reactions of respiration – releasing energy that the cell can use. Most of the energy from respiration is released in
the mitochondria.
, Plant cells VS animal cells
Cell wall, permanent vacuole and chloroplasts can only be found in plant cells. Plant cells store carbohydrates as
starch or sucrose; animals cells store carbohydrates as glycogen. Both plant and animal cells are multicellular.
The cell wall – a layer of non-living material outside the cell membrane. Made mainly of cellulose. tough
material – helps the cell keep its shape. Plant cells – fixed shape; Animal cells – more variable in shape. Plant cell
absorb water, producing an internal pressure that pushes against adjacent cells, giving the plant support. a cell
wall strong enough to resist these pressures. The cell wall is porous not a barrier to water or dissolved
substances freely permeable.
Vacuole – permanent feature of a cell. Filled with a watery liquid called cell sap a store of dissolved sugars,
mineral ions and other solutes. Animal cells do contain vacuoles, but they are only small and temporary.
Chloroplast – absorb light energy to make food in the process of photosynthesis. contain a pigment called
chlorophyll. Cells from a plant that is not green contain no chloroplasts.
Cell structure Function
Cytoplasm A jelly-like material that contains dissolved nutrients and salts and structures called organelles. It is where many of the
chemical reactions happen.
Nucleus Contains genetic material, including DNA, which controls the cell’s activities.
Cell membrane It is permeable to some substances but not to others and so controls the movement of substances in and out of the cell.
Mitochondria Organelles that contains the enzymes for respiration, and where most energy is released in respiration.
Ribosomes Ribosomes tiny structures where protein synthesis occurs.
Chloroplast Organelle that contains the green pigment, chlorophyll, which absorbs light energy for photosynthesis. Contains the
enzymes needed for photosynthesis.
Cell wall Plant and bacterial cell walls provide structure and protection. Only plant cell walls are made from cellulose.
Permanent vacuole Filled with cell sap to help keep the cell swollen
Bacterial cell
Chromosomal The DNA of bacterial cells is found loose in the cytoplasm. It is called chromosomal DNA and is not contained within a
nucleus.
Plasmid DNA Bacteria also have small, closed-circles of DNA called plasmids present in their cytoplasm. Unlike the chromosomal DNA,
plasmid DNA can move from one bacterium to another giving variation.
Flagella Bacteria can have one or more flagella (singular: flagellum). These can rotate or move in a whip-like motion to move the
bacterium.
Explain the importance of cell differentiation in the development of specialized cells.
CELLULAR DIFFERENTIATION
When cells express specific genes that characterise a certain type of cell we say that a cell has become differentiated.
Once a cell becomes differentiated it only expresses the genes that produce the proteins characteristic for that type of cell.
Differentiated cells are important in a multicellular organism because they are able to perform a specialised function in the body. However,
specialisation comes at a cost.
The cost is that the differentiated cells often lose the ability to make new copies of themselves.
Multicellular organisms must therefore retain some unspecialised cells that can replenish cells when needed. These unspecialised cells are
called stem cells.
STEM CELLS
Stem cells are cells in animals that can continuously undergo cell division. There are two types of stem cell:
Embryonic stem cells - These are found in an early embryo. These cells are able to divide continuously. All the genes in an embryonic stem cell
can be expressed so they can give rise to all types of cell. They are important for growth.
Some people find the use of embryonic stem cells ethically unacceptable because it involves the destruction of an early embryo.
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All living organisms are composed of units called cells. Organisms which contains different types of cells are celled multi-cellular.
Characteristics shared by living organisms
Require nutrition plants make their own food; animals eat other organisms
Respire release energy from their food
Excrete get rid of waste products
Respond to stimuli are sensitive to changes in their surroundings
Move by the actions of muscles in animals, and slow growth movements in plants
Control their internal conditions maintain a steady state inside the body
Reproduce produce offspring
Grow and develop increase in size and complexity using materials from their food
Organelles – any of the specialized structures within a cell that perform a specific function (e.g., mitochondria, ribosomes, endoplasmic
reticulum). Organelles in unicellular organisms are the equivalent of organs in multicellular organisms.
Cells – the basic structural, functional, and biological unit of all known organisms. A cell is the smallest unit of life. Cells are often called the
"building blocks of life".
Tissues- a cellular organisational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular
matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of
multiple tissues.
Organs - a group of tissues in a living organism that have been adapted to perform a specific function.
Systems - a group of body organs or structures that together perform one or more vital functions — circulatory system, digestive system,
endocrine system, limbic system, nervous system, reproductive system, respiratory system.
Cell structures and functions
The living material that makes up a cell is called cytoplasm sloppy jelly
– complex material made of different structures which are called
organelles.
The largest organelle in the cell is the nucleus.
Nearly all cells have a nucleus. The few types
which don’t have are usually dead (e.g. the
xylem vessels) or don’t live for very long (e.g.
red blood cells).
Nucleus controls the activities inside the cell. –
contains chromosomes (e.g. in human cells) which carries the genetic material. Genes control the activities in the
cell by determining which proteins the cell can make. The DNA remains in the nucleus, the instructions for
making proteins are carried out of the nucleus to the cytoplasm, where the proteins are assembled on
ribosomes.
One very important group of proteins found in cells are enzymes. Enzymes control the chemical reactions that
take place in the cytoplasm.
All cells are surrounded by a cell membrane. thin layer – forms a boundary between the cytoplasm of the cell
and the outside. partially permeable – small molecules can pass through. When the membrane can control
the movement of some substances selectively permeable.
One organelle that is found in the cytoplasm of all living cells is the mitochondrion. carry out some of the
reactions of respiration – releasing energy that the cell can use. Most of the energy from respiration is released in
the mitochondria.
, Plant cells VS animal cells
Cell wall, permanent vacuole and chloroplasts can only be found in plant cells. Plant cells store carbohydrates as
starch or sucrose; animals cells store carbohydrates as glycogen. Both plant and animal cells are multicellular.
The cell wall – a layer of non-living material outside the cell membrane. Made mainly of cellulose. tough
material – helps the cell keep its shape. Plant cells – fixed shape; Animal cells – more variable in shape. Plant cell
absorb water, producing an internal pressure that pushes against adjacent cells, giving the plant support. a cell
wall strong enough to resist these pressures. The cell wall is porous not a barrier to water or dissolved
substances freely permeable.
Vacuole – permanent feature of a cell. Filled with a watery liquid called cell sap a store of dissolved sugars,
mineral ions and other solutes. Animal cells do contain vacuoles, but they are only small and temporary.
Chloroplast – absorb light energy to make food in the process of photosynthesis. contain a pigment called
chlorophyll. Cells from a plant that is not green contain no chloroplasts.
Cell structure Function
Cytoplasm A jelly-like material that contains dissolved nutrients and salts and structures called organelles. It is where many of the
chemical reactions happen.
Nucleus Contains genetic material, including DNA, which controls the cell’s activities.
Cell membrane It is permeable to some substances but not to others and so controls the movement of substances in and out of the cell.
Mitochondria Organelles that contains the enzymes for respiration, and where most energy is released in respiration.
Ribosomes Ribosomes tiny structures where protein synthesis occurs.
Chloroplast Organelle that contains the green pigment, chlorophyll, which absorbs light energy for photosynthesis. Contains the
enzymes needed for photosynthesis.
Cell wall Plant and bacterial cell walls provide structure and protection. Only plant cell walls are made from cellulose.
Permanent vacuole Filled with cell sap to help keep the cell swollen
Bacterial cell
Chromosomal The DNA of bacterial cells is found loose in the cytoplasm. It is called chromosomal DNA and is not contained within a
nucleus.
Plasmid DNA Bacteria also have small, closed-circles of DNA called plasmids present in their cytoplasm. Unlike the chromosomal DNA,
plasmid DNA can move from one bacterium to another giving variation.
Flagella Bacteria can have one or more flagella (singular: flagellum). These can rotate or move in a whip-like motion to move the
bacterium.
Explain the importance of cell differentiation in the development of specialized cells.
CELLULAR DIFFERENTIATION
When cells express specific genes that characterise a certain type of cell we say that a cell has become differentiated.
Once a cell becomes differentiated it only expresses the genes that produce the proteins characteristic for that type of cell.
Differentiated cells are important in a multicellular organism because they are able to perform a specialised function in the body. However,
specialisation comes at a cost.
The cost is that the differentiated cells often lose the ability to make new copies of themselves.
Multicellular organisms must therefore retain some unspecialised cells that can replenish cells when needed. These unspecialised cells are
called stem cells.
STEM CELLS
Stem cells are cells in animals that can continuously undergo cell division. There are two types of stem cell:
Embryonic stem cells - These are found in an early embryo. These cells are able to divide continuously. All the genes in an embryonic stem cell
can be expressed so they can give rise to all types of cell. They are important for growth.
Some people find the use of embryonic stem cells ethically unacceptable because it involves the destruction of an early embryo.
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