OCR F211 Cells, Exchange and Transport


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Cells, Exchange and Transport
Cell Structure
Light microscope
Use glass lenses to refract light rays to create an image
Most biological specimens are colourless, so we stain them to they are easier to see
- Different cell parts absorb more stain than others so we can distinguish them
Transmission electron microscope
Masses electrons through a thin specimen
Scanning electron microscope
Bounces electrons off a specimen surface coated with large ions
The number of times greater an image is than the actual object
Size of image / Actual size of object
The ability to distinguish between two objects very close together; the higher the resolution, the greater
detail can be seen
Microscope Greatest magnification Greatest resolution
Light x 1400 200 nm
Transmission electron x 300,000 0.5 nm
Scanning electron x 300,000 >0.5 nm
Animal Plant
Nucleus Structure 2 membranes (nuclear envelope), gaps in membrane (nuclear pores)
Function To store DNA in the nucleolus
Endoplasmic Structure Network of membranes, rough ER have ribosomes attached and is usually
continuous with nuclear envelope. Enclosed space called cisternae
Reticulum Function RER: Protein synthesis, polypeptides collected in the cisternae, SER:
hormone production, break down toxins

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Cells, Exchange and Transport
Golgi Structure Stack of curved membranes enclosing flattened sacs, sacs constantly change
when Lysosomes fuse to it
Apparatus Function To process and package proteins
Lysosomes Structure Bags of digestive enzymes
Function To fuse with another vesicles containing something that needs to be broken
down, destroy unwanted or old organelles
Chloroplasts Structure Envelope, contains
grana that forms
stacks called
thykoloid, contain
chlorophyll, stroma
and starch grains
Function Photosynthesis in the
Mitochondria Structure Envelope; inner membrane folded to form cristae
Function Aerobic…read more

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Cells, Exchange and Transport
Cell Membranes
Roles of membranes
Within cells On cell surface
Separates cell components from cytoplasm Cell recognition and signalling
Holds components of some metabolic Regulates transport in and out of cells
pathways in place Separates cell components from the outside
Structure of cell membranes
Fluid mosaic model
Extrinsic proteins: Proteins partially embedded in the bilayer on the face
Intrinsic proteins: Proteins surrounded by the bilayer
Glycolipid: A phospholipid with a carbohydrate part
Glycoprotein: A protein with a carbohydrate part
Phospholipids…read more

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Cells, Exchange and Transport
Protein and glycoprotein
Transport substances
- Channel proteins: for large molecules, very hydrophilic molecules
- Carrier proteins: for ions, active movement
Recognition and communication
- Receptor sites bind with hormones (and drugs)
- Glycoproteins and glycolipids allow self-recognition to the immune system
- Glycoproteins can bind cells together in tissues
Metabolic processes
- Enzymes and coenzymes on membranes where metabolic reactions take place
- E.g.…read more

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Cells, Exchange and Transport
Insulin receptor
Insulin released from beta-cells in islets of langerhans in the pancreas
Insulin attaches to receptors in many cells
Triggers more glucose channels to be present in membrane
Medicinal drugs
Drugs developed to have complimentary shape to a receptor
Some drugs block receptors e.g. beta blockers (prevent increase in heart rate)
Some drugs mimic neurotransmitters e.g. anti-depressants
Viruses and poisons
Viruses bind with receptors in plasma membrane
e.g. HIV attaches to receptors on T-lymphocytes
Some poisons bind with receptors
e.g.…read more

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Cells, Exchange and Transport
Endocytosis: bulk transport of materials into cell
Exocytosis: bulk transport of materials out of cell
- Possible as membranes can fuse, separate and pinch
off, in form of vesicles
- Requires ATP
e.g. Hormones ­ insulin is produces in large quantities in the
pancreatic cells, its processed and packages into vesicles at the
Golgi apparatus. Vesicles then fuse with the plasma membrane
to release insulin into the blood.…read more

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Cells, Exchange and Transport
Cell Division and Cellular Organisation
Cell Cycle
95% of cell cycle in embryo
Normal cell functions still carried out
G1 phase:
Cellular contents (not DNA) duplicated
S phase:
DNA duplicated
Each chromosome now consists of two sister chromatids attached by a centromere
G2 phase:
Checks and repairs DNA
The nuclear division
Takes about one hour
Chromatids become visible by coiling
and super coiling
Centrioles move apart
Spindle fibres start to form
Nuclear membrane breaks down
Spindle…read more

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Cells, Exchange and Transport
Cytoplasm divides
Cell membrane forms a
cleavage furrow and a
contractile ring pulls
membrane together
Plant cells: cell plate
Significance of mitosis
In humans
Used for growth of an embryo and human being
Needed for replacement of damaged or dead cells
e.g.…read more

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Cells, Exchange and Transport
Stem cells
Embryonic stem cells
After the fusion of the gametes, a zygote is formed, which divides into a tiny ball of cells called a
The blastocyst is made up of stem cells
Stem cell: An undifferentiated cell with no hayflick limit that can differentiate into specialised cells
These stem cells as totipotent, they can specialise into any kind of cell
As the embryo forms, the stem cells differentiate into different specialised cells to form the different
tissues and…read more

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Cells, Exchange and Transport
Specialised plant cells
Xylem vessels and phloem sieve tubes
Most plant cells are able to differentiate into other kinds of cells throughout their lives
In the meristem, cells are able to divide at a high rate
- Found just behind the root tip, cells are in various stages of mitosis
A meristem that forms a ring of tissue in the stem is called cambium
- These cells divide to form xylem vessels on the inside of the ring and phloem sieve…read more



This is an amazingly good resource! So much detail, great!

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