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B1: Cells and Organisation (Cells and structures (A bacterium is a single…
B1: Cells and Organisation
Cells and structures
Plant and algal cells also have: cell wall, chloroplast, permanent vacuole
Nucleus
: controls the activities of the cell
Cytoplasm
: where most of the chemical reactions take place
Cell membrane
: controls the passages of substances in and out of the cell
Mitochondria
: where most energy is released in respiration
Ribosomes
: where protein synthesis occurs
Permanent vacuole
: filled with cell sap in plants
Cell wall
: made of cellulose and strengthens plant cells
Yeast is a single-celled organism
The cells have a nucleus, cytoplasm and a membrane surrounded by a cell wall
Chloroplast
: absorb light energy to make food in plants
A bacterium is a single-celled organism
A bacteria cell consists of cytoplasm and a membrane surrounded by a cell wall.
Genes are not distinct in the nucleus; it forms a single DNA loop
Prokaryotic cells consist of cytoplasm and a cell membrane surrounded by a cell wall. Prokaryotes may contain one or more extra small rings of DNA called
plasmids
.
All
bacteria are prokaryotes
Cells may be specialised to carry out a particular function
Eukaryotic cells all have a cell membrane, cytoplasm, and genetic material enclosed in a nucleus
Differentiation
: the process by which cells, tissue, and organs acquire specialised features, especially during embryonic development.
As an organism develops, cells differentiate to form different types of cells
As an animal cell differentiates to form a specialised cell it acquires different sub-cellular structures to carry out a certain function
Animal cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes.
Movement into and out of cells
To get into or out of cells, dissolved substances have to cross the cell membrane
Solutes = particles in a solution eg glucose, sodium ions, chloride ions
Solvent = liquid in which the particles are dissolved, eg water
Solute and solvent molecules move around randomly
Solutes can move into and out of cells by diffusion
Diffusion
is the movement of particles from a higher concentration gradient to a lower concentration gradient
Oxygen required for respiration passes through cell membranes by diffusion
The
greater
the difference in concentration, the
faster
the rate of diffusion
An
increase in temperature
means the gas in a solution move around more rapidly, so diffusion takes place more
quickly
Dissolved substances such as
glucose
,
urea
,
oxygen
and
carbon dioxide
move in and out of cells by diffusion
Osmosis
: the movement of water from a high concentration gradient to a low concentration gradient through a partially permeable membrane
Differences in the concentration of solutions inside and outside a cell cause water to move into or out of a cell by osmosis
Osmosis is important to maintain turgor in plant cells
Animal cells can be damaged if the concentration outside the cell changes drastically
Isotonic
: when the concentration of solutes in the solution outside the cell is
the same
as the internal concentration
Hypertonic
: when the concentration of solutes in the solution outside the cell is
higher
than the internal concentration
Hypotonic
: when the concentration of solutes in the solution outside the cell is
lower
than the internal concentration
Active Transport
: moves substances from a low concentration gradient to a high concentration gradient
Uses energy released from food in respiration to provide the energy required
Allows plant root hairs to absorb mineral ions required for healthy growth from very dilute solutions in the soils
against a concentration gradient
Enables sugar molecules used for cell respiration to be absorbed from lower concentrations in the gut into the blood where the concentration of sugar is higher
Microscope
Light microscopes magnify up to about
x2000
, and have a resolving power of about 200nm
Electron microscopes magnify up to about
x2,000,000
, and have a resolving power of around 0.2nm
Light microscopes use a beam of light to form an image of an object. They are relatively cheap
The invention of the electron microscope allowed biologists to see and understand more about the subcellular structures inside cells
Exchanging materials
Single-celled organisms have a relatively large SA:V ratio so all necessary exchanges with the environment take place over this surface
In multi-cellular organisms, many organs are specialised with effective exchange surfaces
Exchange surfaces usually have a large surface area and thin walls, which give short diffusion distances.
In animals, exchange surfaces will have an efficient blood supply or, for gaseous exchange, be ventilated
The effectiveness of an exchange surface can be increased by:
2) a
thin membrane or being thin
to provide a short diffusion path
3) In animals,
having an efficient blood supply
moves the diffusing substances and maintains a steep concentration gradient
1) A
large surface area
which exchange can take place
4) In animals, being ventilated makes gas exchange more efficient by maintaining steep concentration gradients