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What is the maximum resolution achieved by a TEM microscope?
What is the maximum magnification achieved by a TEM?
What is the maximum resolution achieved by a SEM?
What is the maximum magnification achieved by a SEM?
What is the maximum resolution achieved by a Light Microscope?
What is the maximum magnification achieved by a light microscope?
What is the difference between magnification and resolution?
magnification is the degree to which the size of an image is larger then the image itself whereas resolution is the degree to which it is possible to distinguish between two separate points that are very close together.
Why do we stain biological material?
Most biological material is transparent and so to be able to see it in detail we must add stains. Chemicals in stains bind to other chemicals in/on the specimen allowing us to see it in detail. Some chemicals bind to specific structures e.g. Acetic Orcein which stains DNA red.
How is magnification calculated?
Magnification=Size of Image÷Size of Actual object
What is the function of the nucleus?
The nucleus holds all the cells genetic information in the form of DNA which holds the instructions for protein synthesis.
What is the function of the Nucleolus?
The Nucleolus make RNA and Ribosomes which pass into the cytoplasm and take part in protein synthesis.
What is the function of the nuclear envelope?
the nuclear envelope is a membrane that surrounds the nucleus. It prevents the nucleus and DNA from getting damaged.
What is the function of Rough Endoplasmic Reticulum?
RER transports proteins made by the attached ribosomes.
What is the function of the Smooth Endoplasmic Reticulum?
The SER is involved in making lipids.
What is the function of the Golgi apparatus?
The Golgi Apparatus modifies proteins transported from the RER and packages them into vesicles ready to be transported.
What is the function of ribosomes?
They are the site of protein synthesis.
What is the function of the mitochondria?
ATP is made here. This is the site of respiration.
What is the function of lysosomes?
They contain digestive enzymes that are used to break down material.
What is the function of the chloroplasts?
They are the site of photosynthesis in plant cells.
What is the function of the plasma membrane?
The plasma membrane controls the entry and exit of substances into and out of the cell.
What is the function of the centrioles?
The centrioles form the spindle which moves chromosomes in cell division.
What is the function of the flagella and cilia?
They both move by ATP. The flagella makes the sperm swim while the cilia moves mucus along the trachea in wave like motions.
Outline the process of the production and secretion of proteins?
- 1. The gene containing the instructions for protein synthesis is copied from the DNA onto a molecule of mRNA.
- 2. The mRNA leaves the nucleus through pores in the nuclear envelope and attaches to a ribosome.
- 3. The ribosome reads the code and assembles the protein in order of the code.
- 4. The protein is sent to the Golgi apparatus in vesicles where it is modified and packaged into vesicles.
- 5. The protein diffuses across the cell to the plasma membrane which the vesicle fuses with and then releases the protein outside the cell through exocytosis.
What is the importance of the cytoskeleton?
The cytoskeleton is an internal framework of fibres that gives the cell structure. The cytoplasm contains microfilaments and microtubules to keep the cells shape stable.
What is a microfilament?
A microfilament is a small solid strand of actin that is 7nm in diameter.
What is a microtubule?
A microtubule is a cylinder of Tubulin that is 25 nm in diameter.
Explain the action of Kinesin?
Kinesin attaches one end to an organelle and the other end to a microtubule. Using ATP it swivels which moves the organelle. It then reattaches itself and repeats the process.
Name 4 differences between prokaryotic cells and eukaryotic cells?
- 1. Prokaryotic cells have no nucleus where Eukaryotic cells do.
- 2. Prokaryotic cells have no membrane bound organelles.
- 3. Prokaryotic cells have smaller ribosomes.
- 4. Prokaryotic cells have circular DNA whereas Eukaryotic cells have linear DNA.
What is a cell wall?
A cell wall is present only in plant cells and is a wall of cellulose outside the plasma membrane. The cellulose forms a sieve like network of strands making the cell wall strong.
Why do we stain biological material for use in electron microscopy?
Electron micrographs produce a black and white image. A specialised computing programme is used to add colour to the image.
Outline the structure of the nucleus and the nuclear envelope?
Nucleus - The largest organelle in the cell. When stained darkened patches appear called chromatins. The nucleus is surrounded by the nuclear envelope.
Nuclear envelope - a double membrane with a fluid filled space in between. There are many holes in the envelope called pores which are large enough to allow relatively large molecules to pass through the envelope.
Outline the structure of the Endoplasmic Reticulum?
The ER is a series of membrane bound flattened sacs called cisternae. It is a continuation of the outer nuclear membrane. The rough endoplasmic reticulum has ribosomes attached to it whereas the smooth endoplasmic reticulum has no ribosomes.
Outline the structure of the Golgi apparatus?
The Golgi apparatus is a stack of membrane bound flattened sacs.
Outline the structure of a mitochondria?
A mitochondria has a double membrane between which is a fluid filled space. The internal membrane is highly folded into cristae to provide a high SA for enzymes. The centre of the mitochondria is called the matrix.
Outline the structure of a chloroplast?
Chloroplasts are found in plant cells and some protocist cells. They have a double membrane with a fluid filled space in between. The internal membrane is continuous with a network of flattened membrane sacs called thylakoids. A stack of thylakoids is called a granum. Chlorophyll molecules are present on the thylakoid and intergranal membranes.
Outline the structure of a ribosome, a centriole and a lysosome?
Ribosome - can be free in the cytoplasm or attached to the RER. They are made up of two subunits - 1 large, 1 small.
Lysosome - spherical sac containing a digestive enzyme
Centriole - A centriole is made up of microtubules (protein fibres). There is a pair of centrioles next to the nucleus in animal cells and protoctists.
Outline the role of membranes within and on the surface of cells?
- - seperate the cells components from the outside environment
- - separate the cells components from the cytoplasm
- - control the entry/exit of materials in and out of the cell
- - used in cell recognition/cell signalling.
Describe the structure of a phospholipid?
the phospholipid is made up of a hydrophilic phosphate head - which is attracted to water and 2 hydrophobic fatty acid tails which stay away from water.
What makes a molecule hydrophobic/hydrophilic?
if the charges of a molecule are spread out evenly then the molecule will be hydrophobic. If the charges are spread out unevenly then the molecule will be hydrophilic.
Why are other components needed in biological membranes? Give examples of cells with other components?
- a simple phospholipid bilayer is not capable of performing all the functions of a membrane. Also the bilayer by itself is too fragile to function as a barrier.
- Muscle cells have many channels to allow the maximum uptake of glucose for energy for muscle contraction and plasma membranes of cells in a growing shoot have receptors to detect molecules regulating growth.
What type of barriers are plasma membranes?
Plasma membranes are partially permeable membranes - allow some substances through. All membranes are permeable to water.
What is the fluid mosaic model?
The fluid mosaic model is a model that describes the simple phospholipid bilayer as the fluid giving the membrane basic structure and the various protein molecules as tile like components which give the membrane a 'mosaic' appearance.
What is the difference between a glycolipid and a glycoprotein?
a glycolipid is a phospholipid molecule with a carbohydrate attached to it whereas a glycoprotein is a protein molecule with a carbohydrate attached to it.
What role does cholesterol play in membranes?
Cholesterol gives Eukaryotic cells stability by fitting between fatty acid tails of the phospholipid molecules and preventing molecules such as water or oxygen from directly passing through the bilayer.
What is a carrier protein and give an example of a substance it 'carries'?
A carrier protein transports some substances across the membrane. Sugars e.g. Glucose which are too large and hydrophilic to go through directly are 'carried' through.
What is a channel protein? Give an example of a substance it pumps.
A channel protein actively pumps some substances across the biological membrane. In plant roots, Magnesium is actively pumped from the surrounding soil into the root hair cells using ATP energy. This is important as Magnesium ions are needed for the manufacture of chlorophyll. As the mineral ions enter the cell they decrease the water potential of the cell causing water to enter the cell by osmosis.
What are receptor sites?
Receptor sites can be glycoproteins or glycolipids. They provide a specific site for a hormone to bind to, to produce a cell response. The cell will only respond to hormones that are specific to their receptors.
What are glycoproteins and glycolipids used for?
Glycoproteins and glycolipids can both be receptor sites for a cell. They are both also used in cell signalling and cell recognition by identifying the cell to the body's immune system. Glycoproteins also connect cells together in tissues.
Explain the effect of increasing temperature on cell membranes? Give an example.
Increasing temperature gives particles more kinetic energy leading them to move faster. This increased movement of phospholipids and other components causes the cell to be 'leaky', allowing substances that wouldnt normally be able to cross the membrane into or out of the cell. E.g. sections of beetroot tissue exposed to increasing temperatures release more and more of the red pigment found in the cells. This is due to the damage being done to the plasma membrane and vacuole membrane.
What is cell signalling?
Cell signalling is how cells communicate with each other using signals. Many molecules act as signal - some signal during processes taking place in cells others signal from one cell to others. Cytokines are an example of cell signals.
Outline the role of membrane-bound receptors?
In multlicellular organisms communication between cells is often achieved through hormones - chemical messengers. Hormones bind to specific receptors on target cells to bring about a response in the cell. The receptor is a complementary shape to the hormone.
Describe the relationship between medicinal drugs and receptors?
some medicinal drugs have been developed that are complementary to the shape of a receptor molecule. Beta blockers are drugs that are used to prevent heart muscle from increasing the heart rate in people where an increase could be dangerous.
What is passive transport?
Passive transport is the movement of molecules down a concentration gradient using the molecules kinetic energy and not using ATP.
What is diffusion?
Diffusion is the movement of molecules from a region of high concentration of that molecule to a region of low concentration of that molecule down a concentration gradient.
What is facilitated diffusion?
This is when molecules are too big or are charged and so cannot cross the cell membranes so must use either carrier proetins or channel proteins to move against their concentraion gradients.
Outline how a carrier protein works?
Carrier proteins are shaped so that a specific molecule e.g. glucose can fit into them at the membrane surface. When the molecule fits the carrier protein changes shape so that the molecule can pass through onto the other side of the membrane.
How does a channel protein work?
Channel proteins basically form 'pores' in the membrane which are shaped so that only a specific ion can fit through. Some are 'gated' meaning that they can open and close.
What is active transport?
active transport is the movement of molecules or ions across membranes, which uses ATP to drive proteins pumps within the membrane.
Outline how carrier proteins work using active transport?
Some of the carrier proteins in membranes act as pumps. They are shaped complimentary to their molecule that fit into them and carry large/charged molecules across the membrane. However pumps only transfer specific molecules one way across the membrane and carry them against their concentration gradient. They also carry molecules at a much faster rate than carrier proteins.
Explain how one way flow is ensured using pumps?
As a molecule is carried through the protein uses energy from ATP. this changes the shape so the molecule being carried across the membrane leaves the carrier protein. The molecule cannot enter the carrier protein again as its shape is no longer complementary to the molecule.
Explain what is meant by bulk transport?
Bulk transport is the movement of a large quantity of molecules across a membrane.
Explain the role of ATP in bulk transport?
ATP is used to move the membranes around to from vesicles and is also used to move these vesicles around.
What is endocytosis?
The movement of materials into the cell
What is exocytosis?
The movement of materials out of the cell.
What is osmosis?
Osmosis is the movement of water molecules from a region of high water potential to a region of low water potential, down a water potential gradient, across a partially permeable membrane.
What would happen if a plant and animal cell was left in a solution that had a higher water potential than that of the inside of the cell?
Plant cell - Water would move by osmosis down the water potential gradient into the cell. The cytoplasm and vacuole would swell causing the cell membrane to expand. However the cell wall would not swella and so would prevent the cell from bursting instead making the cell turgid. Osmosis would stop even with the presence of a water potential gradient.
Animal cell - The cytoplasm would swell and so would the cell membrane and eventually the cell would burst - haemolysis.
What would happen if a plant/animal cell was left in a solution that had a lower water potential than the inside of the cell?
Plant cell - Plasmolysis - water moves out of cell by osmosis. cytoplasm and vacuole would shrink. Cell membrane pulled away from cell wall.
Animal cell - cytoplasm would shrink, cell membrane would shrink and cell would shrivel - crenation.
What is the purpose of the cell cycle?
to produce two daughter cells that are genetically identical to the parent cell and therefore able to carry out the same functions as the parent cell.
What is a chromatin?
The DNA molecules wrapped around histone proteins.
What are sister chromatids?
Two chromosomal replicas which are an exact copy of the original, which when separated during mitosis, each one will end up in a different new daughter cell.
Mitosis only occupies a small proportion of the cell cycle, what does the rest of the cell cycle consist of?
The remaining larger portion cell cycle consists of the copying and the checking of the genetic information.
Why is it so important for new cells to be produced?
asexual reproduction - single celled organisms divide to produce two genetically identical daughter organisms.
growth - multicellular organisms grow by producing extra cells
Repair - damaged cells are replaced by new cells that are genetically identical so can perform the same functions.
What are the Four main stages of mitosis?
Prophase, metaphase, anaphase, telophase
What happens in interphase?
what happens in prophase?
- - Chromosomes supercoil and it can be seen they consist of a pair of sister chromatids using a light microscope
- - the nuclear envelope breaks down and disappears
- - a centriole divides into 2 with each daughter centriole moving to opposite poles of the cell forming the spindle, a structure made of protein threads.
What happens in metaphase?
- The chromosomes move to the equator of the spindle and each attach to a spindle fibre by its centromere.
What happens in anaphase?
- - The replicated sister chromatids are separated from each other when the centromere holding them together splits, making each chromatid a chromosome
- - the spindle fibres shorten pulling the sister chromatids further away from each other to different poles
What happens in telophase?
- - as the chromosomes reach the different poles of the cell, a new nuclear envelope forms around each set
- - the spindle breaks down and disappears
- - the chromosomes uncoil and cannot be seen using a light microscope
What is cytokinesis?
The splitting in two of the whole cell
What is different between plant and animal cell mitosis/cytokinesis?
- - Most animal cells will be able to split by mitosis, however in plants only meristem cells can
- - plants do not have centrioles but the tubulin protein threads are made in the cytoplasm
- - in animals cytokinesis begins by "nipping in" the cell membrane from the outside in but in plants a cell plate forms where the spindle equator was and new cell wall/cell membrane material is laid down along cell plate.
What are stem cells?
Stem cells are undifferentiated cells that are capable of becoming any one of the many types of cell in the fully grown organism.
Where are stem cells found and why is there a large interest in them?
Stem cells are found in the bone marrow and there is a large interest in them as scientists hope one day they will be able to be used in medical treatments using an organisms own cells to repair damaged tissue/organs.
Explain the process of budding in yeast?
Cytokinesis in yeast cells occurs by producing a small bud that nips off the cell, producing a new cell. This is budding.
What is a homologous pair of chromosomes?
Chromosomes that have the same gene at the same loci. Members of a homologous pair pair up during meiosis - e.g. diploid organisms produced by sexual reproduction - one from mother, one from father.
How does meiosis differ from mitosis?
- - Meiosis produces haploid cells - cells containing half the number of chromosomes
- - Meiosis produces cells that are genetically different from each other and their parent cell
Where does meiosis occur?
The sex organs
What is differentiation?
The changes occurring in cells of a multicellular organism so each different type of cell becomes specialised to perform a specific function.
What are the three types of change a cell can undergo as a result of differentiation?
- - The number of a particular organelle
- - The shape of the cell
- - Some of the contents of the cell
Explain what happens to cells that differentiate to become erythrocytes?
- - They lose their nucleus, mitochondria, golgi apparatus and RER
- - They become packed full with the protein haemoglobin
- - Their shape changes to a biconcave disc
How are sperm cells specialised?
- - They contain many mitochondria for movement of undulipodium
- - The sperm head contains a special lysosome - acrosome - which releases enzymes on outside of egg to penetrate it for fertilisation
- - The sperm cells are very long, thin and small to help ease movement
- - The long undulipodium helps propel the sperm cells up the uterine tract towards the egg
How do cells destined to become neutrophils differentiate?
- - They keep their nucleus
- - Cytoplasm appears granular as it is filled with lysosomes with the necessary enzymes needed to kill microorganisms
Define a tissue, an organ and an organ system?
- tissue - a collection of cells that are similar to each other and perform a common function
- organ - a collection of tissues working together to perform a common function
- organ system - a system made up of a number of organs working together to perform an overall life function
Give 2 examples of; tissues/ organs and organ systems. One of a plant and one of an animal?
- Tissue - plant - xylem/phloem, animal - epithelial/nervous
- Organ - Plants - leaves, animals - liver
- Organ system - excretory system/reproductory system
Where do xylem and phloem come from?
dividing meristem cells called cambium
What does xylem tissue consist of?
xylem vessels with parenchyma cells and fibres. Meristem cells produce small cells that elongate and whose walls become reinforced/waterproofed by deposits of lignin. The lignin kills the cells contents, causing the ends of the cells to break down so they become continuous long tubes with a wide lumen.