Biology
Cells
Eukaryotes, organisms made up of a cell containing DNA inside a recognisable nucleus, with
inside one or more linear chromosomes.
Single-celled organism, organism that consists of only one cell.
Multicellular organisms, organism made up of many different cells.
Plant cells tend to be larger than animal cells.
Sub-cellular components, features present in cells
Sub-cellular Structure and description Function
component
Cell membrane A partially permeable layer that Contains the cell contents and
forms a boundary around the controls the movement of
cytoplasm of the cell. substances into and out of the
cell.
Chromosomal DNA One or more linear pieces of double- Stores the genetic material
stranded DNA. required for the various cell
processes.
Cytoplasm Salt ions and sugar molecules are Is the site of chemical
dissolved in it. Fat molecules and reactions and contains
proteins are suspended in it. It also enzymes that control these
contains food reserves reactions. It holds the cell
(ex glycogen in animal cells, starch in organelles.
plant cells) and organelles.
Nucleus Usually round or oval, contained by Regulation of cell functions
two nuclear membranes and through production of RNA
containing DNA in the form and protein required for cell
of chromosomes. It is found inside processes, like cell division,
the cytoplasm. cell differentiation and cell
metabolism.
Mitochondrion A small organelle with an inner and Controls the production and
outer membrane. The inner release of ATP (usable energy)
membrane has many inward- from aerobic respiration.
pointing folds.
Cell wall (plant only) A tough, rigid layer surrounding the Provides a rigid external coat
cell membrane made primarily of to plant cells, providing
cellulose. It is freely permeable to mechanical strength which
water and salts. allows cells to resist bursting
when the cell is turgid.
Chloroplast (plant A small organelle with its own double Traps (absorbs) light energy
only) membrane, found in the cytoplasm and converts it to chemical
of photosynthetic plants, containing energy by the process
chlorophyll and other pigments. of photosynthesis.
Vacuole (plant only) A fluid-filled space surrounded by a Stores water-soluble
membrane in plant cells. The fluid is chemicals and ions and helps
called sap, which is a watery solution to keep plant cells and
, of sugars and salts. In some cells it is tissues firm.
also colored.
Movement across membranes
Passive transport, no energy required ex diffusion and osmosis
Active transport, energy required
Diffusion, ions moving between concentration gradients ex oxygen, glucose and water
Factors affecting the rate of diffusion:
1. Concentration gradient
2. Temperature
3. Distance
4. Size of the particles
5. Surface area
Osmosis, movement of water from a region of higher water potential (dilute solution) to a
region of lower water potential (concentrated solution) through a partially permeable
membrane.
Turgid, cytoplasm is pressing against the cell wall
Flaccid, cytoplasm is shrinking away from the cell wall.
Active transport, movement of particles through a cell membrane from a region of lower
concentration to a region of higher concentration (opposite direction to diffusion) using the
energy from respiration, ATP.
Cell division and sex determination
Mitosis, process of cell division in eukaryotic cells which results in growth form one zygote
When a cell divides by mitosis:
1. Nucleus breaks down
2. DNA is split into two new, identical nuclei.
3. Cytokinesis, cell splits into two new daughter cells
The cell cycle:
1. Interphase, preparation for mitosis
- cell grows
- chromosomes in the nucleus are replicated
- cell respires to provide energy for mitosis.
2. Mitosis
Characteristic Mitosis Meiosis
Number of daughter 2 4
cells produced?
Daughter cells Yes No
genetically identical to
parent cell?
Daughter cells Yes No
genetically identical to
each other?
Chromosome number in The same number as the parent Half the number of the parent cell
daughter cells? cell, diploid if parent cell is diploid haploid
or haploid if parent cell is haploid
When used? Growth, tissue repair, Gamete formation during sexual
replacement of worn-out cells, reproduction
Cells
Eukaryotes, organisms made up of a cell containing DNA inside a recognisable nucleus, with
inside one or more linear chromosomes.
Single-celled organism, organism that consists of only one cell.
Multicellular organisms, organism made up of many different cells.
Plant cells tend to be larger than animal cells.
Sub-cellular components, features present in cells
Sub-cellular Structure and description Function
component
Cell membrane A partially permeable layer that Contains the cell contents and
forms a boundary around the controls the movement of
cytoplasm of the cell. substances into and out of the
cell.
Chromosomal DNA One or more linear pieces of double- Stores the genetic material
stranded DNA. required for the various cell
processes.
Cytoplasm Salt ions and sugar molecules are Is the site of chemical
dissolved in it. Fat molecules and reactions and contains
proteins are suspended in it. It also enzymes that control these
contains food reserves reactions. It holds the cell
(ex glycogen in animal cells, starch in organelles.
plant cells) and organelles.
Nucleus Usually round or oval, contained by Regulation of cell functions
two nuclear membranes and through production of RNA
containing DNA in the form and protein required for cell
of chromosomes. It is found inside processes, like cell division,
the cytoplasm. cell differentiation and cell
metabolism.
Mitochondrion A small organelle with an inner and Controls the production and
outer membrane. The inner release of ATP (usable energy)
membrane has many inward- from aerobic respiration.
pointing folds.
Cell wall (plant only) A tough, rigid layer surrounding the Provides a rigid external coat
cell membrane made primarily of to plant cells, providing
cellulose. It is freely permeable to mechanical strength which
water and salts. allows cells to resist bursting
when the cell is turgid.
Chloroplast (plant A small organelle with its own double Traps (absorbs) light energy
only) membrane, found in the cytoplasm and converts it to chemical
of photosynthetic plants, containing energy by the process
chlorophyll and other pigments. of photosynthesis.
Vacuole (plant only) A fluid-filled space surrounded by a Stores water-soluble
membrane in plant cells. The fluid is chemicals and ions and helps
called sap, which is a watery solution to keep plant cells and
, of sugars and salts. In some cells it is tissues firm.
also colored.
Movement across membranes
Passive transport, no energy required ex diffusion and osmosis
Active transport, energy required
Diffusion, ions moving between concentration gradients ex oxygen, glucose and water
Factors affecting the rate of diffusion:
1. Concentration gradient
2. Temperature
3. Distance
4. Size of the particles
5. Surface area
Osmosis, movement of water from a region of higher water potential (dilute solution) to a
region of lower water potential (concentrated solution) through a partially permeable
membrane.
Turgid, cytoplasm is pressing against the cell wall
Flaccid, cytoplasm is shrinking away from the cell wall.
Active transport, movement of particles through a cell membrane from a region of lower
concentration to a region of higher concentration (opposite direction to diffusion) using the
energy from respiration, ATP.
Cell division and sex determination
Mitosis, process of cell division in eukaryotic cells which results in growth form one zygote
When a cell divides by mitosis:
1. Nucleus breaks down
2. DNA is split into two new, identical nuclei.
3. Cytokinesis, cell splits into two new daughter cells
The cell cycle:
1. Interphase, preparation for mitosis
- cell grows
- chromosomes in the nucleus are replicated
- cell respires to provide energy for mitosis.
2. Mitosis
Characteristic Mitosis Meiosis
Number of daughter 2 4
cells produced?
Daughter cells Yes No
genetically identical to
parent cell?
Daughter cells Yes No
genetically identical to
each other?
Chromosome number in The same number as the parent Half the number of the parent cell
daughter cells? cell, diploid if parent cell is diploid haploid
or haploid if parent cell is haploid
When used? Growth, tissue repair, Gamete formation during sexual
replacement of worn-out cells, reproduction
