Studied by 2 people
The cell vacuole
Sac in plant cells surrounded by tonoplast with a selectively permeable membrane, contains sap.
Vacuoles in animal cells are small and impermanent
Cell Surface Membrane
Partially permeable phosphylid bilayer containing lipids and proteins, the bilayer is in constant motion
Controls the exchange of materials between the external and internal environment acting as a selective and protective barrier
Provides structure and support in holding cell shape
Facilitates cell to cell communication
Mitochondria
double membrane, inner one folded to form cristae which creates a matrix containing ribosomes and DNA
Aerobic respiration takes place here, also the site for oxidative phosphorylation
Golgi Vesicles
membrane bound, fluid filled sacs that are dense near the edges
To store and transport modified proteins and lipids from Golgi apparatus to cells
Rough endoplasmic reticulum
surface covered in ribosomes formed from continuous folds of membrane alongside the nucleus envelope
Processes and folds proteins made by the ribosomes to send to Golgi apparatus
Ribosomes
Small with two subunits, the only organelle that is not membrane bound and floats freely in the cytoplasm (a couple can be bound)
They receive genetic information, read messenger RNA and use instructions to make proteins
Smooth endoplasmic reticulum
No ribosomes on the surface
Involved in production, processing, and storage of lipids and carbohydrates
Chloroplast
Surrounded by a double membrane that binds thylakoids containing chlorophyll that form grand structures, joined by lamellae
Site of photosynthesis and sometimes protein synthesis
The cell wall
Freely permeable to most substances and formed outside the cell membrane, containing narrow threads of cytoplasm connecting to neighbouring cells
Provides structural support, using polysaccharide cellulose in plants and peptidoglycan in bacteria
Golgi apparatus
a stack of curved membranes filled with fluid near the nucleus, with two different faces to carry out different functions
Packages proteins and lipids into Golgi vesicles and makes lysosomes
Lysosomes
Small round membranous vesicles formed by the Golgi apparatus that float freely outside the nucleus.
Outer lysosomal membrane surrounding an acidic interior fluid and hydrolytic enzymes
Break down cell waste such as debris, old organelle and foreign invaders. Also regulate cellular death and metabolism
Nucleus
separated from cytoplasm by nuclear envelope which has many pores and contains chromatin to make up chromosomes and proteins
Regions called nucleolus are darkly stained sites of ribosome production
Houses genetic production, stores chromosomes, is the site for ribosome production and controls/ regulates the activity of the cell such as DNA replication and transcription
What is cell fractionation
Cells are taken part and major organelles are separated from subcellular structures
What happens during homogenisation
Cells are broken apart in a blender and the resultant fluid is filtered to remove any whole cells, this is to create a homogenate that can be split into liquids that are dense in specific organelles.
What is the effect on the tissue when placed in a cold solution, buffer solution or solution of the same water potential?
cold - reduces enzyme activity that breaks down organelles
buffer - pH changes won’t impact organelle structure or function
same water potential - no osmotic loss or gain, organelles will not burst or shrink
What are the stages of cell fractionation?
Small piece of tissue is collected
Tissue is blended to break down cells in order to create homogenate
Homogenate is filtered to remove any remaining whole cells or debris
Homogenate is spun at a slow speed and a solution mainly consisting of nuclei becomes separate, this is removed.
This process is repeated with the supernatant (remaining solution) at a faster rate each time, each time smaller organelles are collected
What effect does increasing the speed of the centrifuge have?
The centrifuge is a tube containing the homogenate and depending on the speed at which it is spun different organelles will be collected, the faster it is spun, the smaller the organelles collected will be.
What does calibrate mean?
To correlate the readings of an instrument with those of a standard in order to check the instruments accuracy
What is the ocular measurement?
The image size - corresponds to different lengths depending on the objective lens being used.
Where is the ocular micrometer and the stage micrometer found ?
Ocular micrometer - embedded in the eyepiece
Stage micrometer - a slide with a small scale of known length.
What the other name for an ocular micrometer?
An eyepiece graticule
What is a DNA nucleoid ?
Where genetic information of a prokaryote is stored. Floats freely in the cytoplasm not associated with history proteins. Does not contain introns (non-coding sections of DNA)
What makes up the cell wall in plant cells fungi cells and prokaryotes.
Plant cell - cellulose
Fungi cell - chitin
Prokaryote - murein a glycoprotein
What is a plasmid?
Extra DNA in a prokaryote. They are tiny circles and can code for properties such as antibiotic resistance. They can be transferred from one to another.
What type of ribosomes are found in eukaryotes and prokaryotes?
Eukaryotes - 80s
Prokaryotes - 70s
How large are viruses?
20 - 300 nm
What nucleic acids do viruses contain?
DNA + RNA
What are attachment proteins for?
To identities and attach to host cells
What does the cell theory state?
All living things contain viruses
What encloses the viral genome?
The capsid - used to protect viral RNA and DNA.
What does the capsid do?
Attaches and penetrates host cells
What is the cell cycle?
Process a cell goes through to copy itself
What is mitosis?
The division stage of the con cycle where the two daughter cells are produced.
Around 11%
Why are daughter cells genetically identical to parent cells?
→ To maintain chromosome number
→ To replace/repair damaged cells and perform the same function
→ Allows asexual reproduction
When would daughter cells not be genetically identical to parent cells?
Genetic mutation
What are the stages of the cell cycles?
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis (extra)
What happens during interphase?
The cell is not dividing
Chromosomes aren't visible
DNA is in the form of chromatin which appears as a dark mass in the nucleus
DNA replicates
What happens during prophase?
part of mitosis
Chromosomes become visible
Nuclear membrane and nucleolus break down
Centrioles move to opposite poles of the cell
Spindle fibres develop from centrioles
What happens during metaphase?
Part of mitosis
Spindle fibres attach to the chromatids at the centromere
Chromatids line up in the middle of the cell
What happens during anaphase?
Part of mitosis
Spindle fibres contract and pull individual chromatids apart at the centre
Chromatids move to opposite poles of the cell
Energy required is provided by aerobic respiration in mitochondria, which gather around spindle filores
What happens during telophase?
Part of mitosis
Spindle fibres disappear
Nuclear membrane forms and surrounds the chromosomes at opposite ends of the cell
Chromosomes become indistinct
Nuclear envelope and nucleolus re-form
What happens during cytokinesis?
Division of the cytoplasm
Forms two daughter cells, between which organelles and cytoplasm are equally distributed
What is the aim of practical 2: root squash to observe mitosis?
To be able to prepare and stain a root tip to observe the stages of mitosis under a microscope
Why macerate the sample?
To make it one cell thick so light can shine through and make mitotic cells visible
Why is HCI used?
To break down middle lamella to make observation of individual cells easier, and to stop biological processes
What is the calculation for mitotic index?
Number of cells undergoing mitosis / total number of cells
What is the maximum useful magnification of an optical microscope?
About x1500
What are the characterising of a transmission electron microscope?
beam of electrons is transmitted through the specimen
Specimen is studied in a vacuum therefore must be dead
Produces a 2-D black-and-white image
Denser areas may appear darker
Specimen must be incredibly thin <100nm
Resolution of roughly 0.1nm
What are the characteristics of a scanning electron microscope?
beams of electrons hit the surface Of the specimen and bounce off
Can produce a 3-D image
Always black-and-white and white
Won’t show any internal structures
Takes place in a vacuum so can only study dead specimens
Why do light microscopes have a lower resolution than electron microscopes?
Light has a longer wavelength than electrons that have a short wavelength
What are the main roles of the cell membrane?
To keep all cellular components inside the cell
Allows selected molecules inside the cell
Organelles from the cytoplasm allowing separate processes to take place
Site for biochemical Reactions
How do phospholipids arrange themselves in a cell membrane?
In a bilayer
What makes up a phospholipid?
fatty acid chains and a phosphate
What are the three different types of proteins that make up 25 to 75% of a cell membrane?
Intrinsic protein - span the whole width of a membrane
Extrinsic protein - Confined to inner or outer surface of membrane
Glycol proteins - Attached to carbohydrate chains
What characteristics of the fluid mosaic model gave it its name?
Fluid - Phospholipids can move giving it a flexible structure
Mosaic - Proteins embedded in the bilayer vary in shape and pattern
What are channel and carrier proteins?
They allow molecules to move through the membranes. Channel proteins allow a passive movement whereas carry a proteins require energy.
What is cholesterol?
A type of lipid with the molecular formula C27H46O, with hydrophobic and hydrophilic interactions pulling phospholipids together
What is the role of cholesterol in the cell membrane?
To provide stability and reduce permeability.
To provide stability and reduce permeability.
What is simple diffusion?
Small non-polar molecules in a high concentration on one side of the membrane can easily pass through the bilayer eg. Hormones and CO2
What is facilitated diffusion?
Polar or large molecules cannot pass straight through the bilayer. Carrier/channel proteins allow molecules to pass through passively
What 6 factors affect diffusion?
→ temperature
→ Distance
→ Surface Area
→Molecule size
→ Concentration gradient
→ Availability of channel/carrier proteins
What are the characteristics of active transport?
needs ATP - produced in mitochondria
If diffusion can't meet cell needs
Through carrier proteins to pump across membranes
What are the characteristics of passive transport?
No energy required
To transport molecules from high to low concentration
Examples of active transport
Uptake of glucose and amino acids in small intestine
Loading of companion cells in phloem
Excretion of hydrogen ions and urea by kidneys
What is a substance that dissolves called?
A solute
What is a solid dissolved in a liquid called?
A solution
What is water potential?
The tendency of water molecules in a system to move
What is the unit for water potential?
KPa
What substance has the highest water potential, zero?
Water - everything else will have a negative water potential
What is osmosis?
The movement of water from a region of high water potential to low water potential
What determines the net movement of osmosis?
The differences in water potential into solutions connected by partially permeable membrane
Which proteins allow osmosis to take place?
Channel proteins
What’s an isotonic solution?
Same solute concentration as the cytoplasm of the cell
What’s a hypertonic solution?
Higher solute concentration than the cytoplasm of the cell, Osmosis occurs out of the cell
What’s a hypotonic solution?
Lower solute concentration than the cytoplasm of the cell, Osmosis occurs into the cell
What is cytolysis?
When the cell swells and bursts due to osmosis
What is crenation?
When the cells shrivel due to osmotic loss
How can you increase rate of movement across a membrane?
microvilli along epithelial cells increase surface area for insertion of carrier proteins
Increased density of carrier and channel proteins in a given area of membrane
What is the role of diffusion in absorption?
Throughout continuous digestion of carbs and proteins there is usually a higher concentration of them in the ileum than the blood creating a concentration gradient
Due to the constant circulation of blood, the glucose in it can be continuously removed by cells for respiration, maintaining concentration
What is the role of active transport in absorption?
at best diffusion can make an equal concentration gradient, not all available glucose and amino acids can be absorbed this way
To prevent them passing out the body they can also be absorbed by active transport
This is an example of co-transport because they are drawn into cells along with sodium ions being transported out by the Na-K pump
How does co-transport of a glucose molecule work?
sodium ions are transported into the blood blood through carrier protein
This maintains higher concentration gradient of sodium ions in the lumen
Sodium ions diffuse into epithelial cells through a different protein carrier, carries glucose and amino acids with them
Glucose and amino acids pass into plasma by facility to diffusion using another type of carrier
What type of transport is the movement of glucose?
Indirect active transport, glucose moves against the concentration gradient however it is powered by the sodium ions Moving down the concentration gradient
Why is the term co-transport used to describe the movement of glucose and amino acids?
Because glucose and amino acids are drawn into cells along with sodium ions by the sodium potassium pump
What does ATP stand for?
adenosine triphosphate
What is ATP?
A nucleotide made up of an adenine base, a ribose sugar and 3 phosphate groups
What happens when ATP breaks down
Energy is released and adenine diphosphate or adenine monophosphate is formed
What enzyme breaks down ATP?
ATP hydrolase
What enzyme makes adenine triphoshate?
ATP synthase
Where does the energy for active transport come from?
ATP
Where is active transport performed?
Specific carrier proteins in the cell membrane
What are the stages of active transport?
Molecule binds to carrier protein at receptor site
ATP binds on other side and splits, releasing energy
Protein opens on opposite side
Molecule released
ATP is reformed and protein reverts to original shape
Name 3-5 examples of active transport
Absorption of amino acids from gut to blood
Absorption of mineral ions by roots
Exchange of Na+ and K+ ions, allowing conduction of nerve impulses and glucose transport
Endocytosis - cells ingest external fluid
Exocytosis - cells release substances through a vesicle that fuses with the membrane
Name 4 factors that affect the rate of active transport
density of carrier proteins
Speed of carrier proteins
ATP availability
Any factors affecting rate of respiration
Note 
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