AS Biology Unit 1 (F211) - Cells, exchange and transport (OCR)

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Preview of AS Biology Unit 1 (F211) - Cells, exchange and transport (OCR)

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Studying and measuring cells
Viewing Cells:
Magnification the size of an object is larger than the object itself
Resolution to distinguish between two objects that are close to each other (higher the resolution
= higher the detail)
Staining
You must add a stain, as most biological matter is transparent, stains include:
iodine solution stains starch grains black, everything yellow
methylene blue stains the nuclei blue
Sectioning
When sectioning it must be in thin slices, allowing a beam of light to pass through. They MUST be in
embedded in wax, as it makes it easier to identify tissue
Light and electron microscope
Characteristic Light Microscope (LM) Electron Microscope (EM)
Wavelength Light; 400 nm Electron beam; 1.0 nm
Resolution 200 nm 0.5 nm
Magnification X1500 X250,000 (TEM)
X100,000 (SEM)
Image Coloured if dyes/stains used 2D (TEM)
3D (SEM)
Black and white
Specimens Living or non-living Non-living
Advantages Living processes can be followed Very high resolution
Disadvantages Samples can be prepared quickly Very expensive
Cells and organelles
Organelles
Organelles Functions Key points

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Mitochondria Aerobic respiration Folded internal membrane to give large surface
area
Chloroplast Photosynthesis Stacks of membranes for large surface area for
pigments
Nucleus Contains genetic info of Separated by nuclear envelope with pores for
chromosomes communication
Nucleolus Production of ribosome Dark staining area in nucleus
Ribosome Amino acid assembled On the RER (rough endoplasmic reticulum or free in
to make proteins cytoplasm)
Rough Endoplasmic Place where ribosome Covered in ribosome
Reticulum (RER) transport proteins to
Golgi Apparatus
Smooth Makes fats, No ribosome on surface
Endoplasmic…read more

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Lysosome Enzymes kill of Membrane keeps enzymes separate from rest
pathogens of the cell
Cilia Moves materials
alone tubes
Cilia and undulipodium have the same internal
structure arrangement of 9+2
Undillipodium/Flagellum Moves sperm cells
and gametes of some
plants
Cytoskeleton supports structure and moves organelles around eukaryotic cells
Prokaryote and Eukaryote
Feature Prokaryotic cells Eukaryotic Cells
Animal Cells Plant Cells
Nucleus
Cell wall (not cellulose) (cellulose)
Mitochondria
Chloroplast
Golgi Apparatus (vesicles) (tonoplast)
Endoplasmic Reticulum
Vacuoles (some)
Pili & Flagella
Undilipodia & Cilia (some) (gametes)
Size…read more

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Carbohydrates are attached to protein and lipid and face the outside of the cell. All this makes
the fluid mosaic model.
Why fluid mosaic?
Fluid: phospholipids are liquid and free to move
Mosaic: lots of components put together like a mosaic
Functions
Components
of Cell
Membrane
Phospholipids Form a bilayer that acts as a barrier between cytoplasm and cell outside
Fluid so components can move within the membrane
Permeable to non-polar molecules e.g. oxygen
Permeable to small polar molecules e.g.…read more

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Diffusion:
Diffusion occurs passively ­ no ATP is needed as substances move down the concentration
gradient. Molecules such as oxygen and carbon dioxide diffuse easily across the bilayer as they are
small and uncharged
Osmosis:
Osmosis is a form of diffusion. Although water molecules are polar they are small enough to pass
through the bilayer. Osmosis is the movement of water in and out the cells.…read more

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Cell signalling and investigating cell membranes
Cell signalling
Cells communicate with one another by cell signalling, three ways in which to do so are:
Neurones they transmit information electronically over long distance
Hormones endocrine secrete hormones into the bloodstream, they have effects on target cells
which are the only cells that detect the hormone and respond.…read more

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Mitosis
S stage - replicates DNA
G stage ­ cells build up energy reserve and makes new membranes
As a result of mitosis: the number of chromosomes stay the same, genetic info passed on is
identical in the daughter cells, two nuclei are formed, and no genetic variation occurs
Stages of mitosis
Prophase: chromosomes shorten and thicken, easy for the cell to move chromosomes around.
Chromosomes are now condensed, the nuclear envelope breaks up.…read more

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Distances from the surfaces to the centre are too great
Surface area to volume ratios
An example of that are the alveoli, they have a large surface area and thin layer that has a short
distance for diffusion, a good supply of blood in the capillaries to absorb and/or deliver waste
substances
In lungs, oxygen diffuses from the air in the alveoli in the blood. Carbon dioxide goes in the reverse
direction, this is the gas exchange.…read more

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Ciliated cells Squamous eplitilihum
Move mucus up the airways towards the Gives short diffusion pathway for oxygen and
mouth carbon dioxide in the alveoli
Measuring lung activity
Tidal volume ­ volume breathed into the lungs in one breath
Vital capacity ­ maximum volume of air that can be breathed out of lung after taking a
deep breath
Breathing rate/breaths per minute = number of peaks per minute on graph
Mean tidal volume= mean of several tidal volumes from graph
Ventilation rate = volume of air…read more

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Very small = large surface area
Vein Walls are thin, as blood pressure is low
Walls stretch to accommodate large volumes of blood
Veins have semilumar valves ensuring blood travel
towards heart
Lined by endothelium cells
Semilunar valves in veins Muscles of body contract and squeeze veins, pushing
blood to heart
Pressure of blood forces valve open
Backflow of blood closes the valve
The heart and cardiac cycle
Heart is cardiac cycle, which is myogenic (contracts of its own accord).…read more

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