(AS) Cell structure Flashcards
How do you prepare a microscope slide?
- Cut a very thin layer of the tissue that is going to be examined.
- Staining the tissue to allow for easier viewing under a microscope.
- Permanently mount the specimen on a clean glass slide for repeated use.
- Lower the coverslip onto the specimen to prevent the specimen from drying out.
How do you prepare a microscope slide using a liquid specimen?
- Add a few drops containing the liquid sample to a clean slide using a pipette.
- Lower a coverslip over the specimen and gently press down to remove air bubbles. The coverslip also protects the microscope lens from liquids and help to prevent the specimen from drying out.
How do you prepare a microscope slide using a solid specimen?
- Use scissors or a scalpel to cut a small sample of tissue, and peel away or cut a very thin layer of cells from the tissue sample. You need to ensure that the samples are thin enough to allow light to pass through.
- Pace the sample onto a slide. A drop of water may be added at this point.
- Apply iodine stain to make the specimen more visible under the microscope.
- Gently lower a coverslip over the specimen and press down to remove any air bubbles.
How do you prepare a slide using human cells?
- Brush teeth thoroughly with a normal toothbrush and toothpaste. This removes bacteria from teeth, so they don’t obscure the view from the cheek cells.
- Take a sterile cotton swab and gently scrape the inside cheek surface of the mouth for 5-10 seconds.
- Smear the cotton swab on the centre of the microscope slide for 2-3 seconds.
- Add a drop of methylene blue solution. This solution stains negatively charged molecules in the cell, including DNA and RNA. This causes the nucleus and mitochondria to appear darker than their surroundings.
- Place a cover slip on top. Lay the coverslip down at one edge and then gently lower the other edge until it is flat. This reduces bubble formation under the coverslip.
- Absorb any excess solution by allowing a paper towel to touch one side of the coverslip.
What is the purpose of stains?
Stains allow transparent or difficult to distinguish structures such as the cytoplasm to be viewed clearly under a light microscope.
What are the uses of iodine stain?
Stains starch blue-black, and colours nuclei and plant cells pale yellow.
What are the uses of methylene blue stain?
Stains animal cell nuclei dark blue.
What are the uses of crystal violet stain?
Stains cell walls purple.
What are the uses of congo red stain?
Is not taken up by cells and stains the background red, so provides contract with any cells present.
What is a biological drawing?
To record the observations seen under a microscope, a labelled biological drawing is often made. Biological drawings are line drawings which show specific features that have been observed when the specimen was viewed.
What are the rules and conventions of a biological drawing?
The drawing must have a title, the magnification under which the observations are show by the drawing should be recorded if possible (a scale bar may be used), a sharp pencil should be used, drawings should be on plain white paper, lines should be clear, single lines with no sketching, no shading should be used, the drawing should take up as much of the space on the page as possible, well-defined structures should be drawn, only visible structures should be drawn and the drawing should look like the specimen, the drawing should be made with proper proportions, structures should be clearly labelled with lines that do not cross, do not have arrowheads, connect directly to the part of the drawing being labelled, are on one side of the drawing and are drawn with a ruler.
What are plan biological drawings?
Drawings of cells are typically made when visualising cells at a higher magnification power, whereas plan drawings are typically made of tissues viewed under lower magnifications so individual cells are never drawn on plan diagrams, instead a group of cells is often represented just by separating the cell with lines.
What is magnification?
Magnification is the number of times that a real-life specimen has been enlarged to give a larger view. The magnification (M) of an object can be calculated if both the size of the image (I) and the actual size of the specimen (A) is known. Magnification = Image size / actual size.
What are the steps for a magnification calculation?
- Rearrange the equation.
- Read and measure the relevant values from the question or any images provided.
- Convert any units.
- Substitute numbers into the rearranged equation and consider whether this value makes sense in the context provided.
What are the conversions between millimetres, micrometres and nanometres?
Cellular structures are usually measured in either micrometres (μm) or nanometres (nm), while any measurements in an exam with a ruler are likely to be in millimetres (mm). There are 1000μm in 1mm and there are 1000nm in 1μm.
What is an eyepiece graticule?
An eyepiece graticule and stage micrometre are used to measure the size of an object when viewed under a microscope. The eyepiece graticule is an engraved ruler that is visible when looking through the eyepiece of a microscope. Eyepiece graticules are often divided into 100 smaller division known as graticule divisions or eyepiece units.
The values of the divisions in an eyepiece graticule vary depending on the magnification used, so the graticule needs to be calibrated every time an object is viewed. The calibration is done using a stage micrometre; this is a slide that contains a tiny ruler with an accurate known scale.
How would you calculate the magnification factor using an eyepiece graticule and a stage micrometre?
In the diagram, two stage micrometres divisions of 0.1mm (100µm) are visible. Each 100µm division is equal to 40 eyepiece graticule divisions. 40 graticule divisions = 100µm
1 graticule division = number of µm / number of graticule divisions.
1 graticule division = 100µm / 40 eyepiece graticule visions = 2.5; this is the magnification factor.
What is the resolution of a microscope?
The resolution of a microscope is its ability to distinguish two sperate points on an image as separate objects. This determines the ability of a microscope to show detail.
What is the resolution of a light microscope?
The resolution of a light microscope is limited by the wavelength of light. Visible light falls within a set range of light wavelengths; 400-700nm. The resolution of a light microscope cannot be smaller than half of the wavelength of visible light. Therefore, the shortest wavelength of visible light is 400nm, so the maximum resolution of a light microscope is 200nm.
What is the resolution of an electron microscope?
Electron microscopes have a much higher resolution, and therefore magnification than light microscopes. This is because electrons have a much smaller wavelength than visible light. Electron microscopes can achieve a resolution of 0.5nm.
Why is the resolving power of electron microscopes greater than that of light microscopes?
The resolving power of electron microscopes is much greater than that of light microscopes due to the smaller wavelength of electrons in comparison to visible light.
What types of specimens are light microscopes used for?
Light microscopes are used for specimens larger than 200nm. They shine light through the specimen and the specimens can be living (therefore moving) or they can be dead. Light microscopes are useful for looking at whole cells, small plant and animal organisms, and tissues within organs such as in leaves or in skin.
What types of specimens are electron microscopes used for?
Electron microscopes, both scanning and transmission, are used for specimens larger than 0.5nm. Electron microscopes fire a beam of electrons at the specimen. Transmission electron microscopes fire electrons through a specimen and scanning electron microscopes bounce electrons off the surface of a specimen. The electrons are picked up by an electromagnetic lens which then shows the image. Electron microscopy requires the specimen to be dead, meaning they can only be used to capture a snapshot in time and not active life processes as they occur. Electron microscopes are useful for looking at organelles, viruses and DNA as well as looking at whole cells in more detail.
What are some characteristics of light microscopes?
Small and portable
No vacuum required
Specimen preparation can be simple
Maximum magnification of 2000x
Maximum resolution of 200nm
Specimens can be living or dead
What are some characteristics of electron microscopes?
Large machines that are permanently installed in laboratories
Need to create a vacuum for electrons to travel through
Specimen preparation is complex
Maximum magnification of 500 000x
Maximum resolution of 0.5nm
Specimens are always dead
What are the two types of cells?
Eukaryotic and prokaryotic.
What is the different in ultra structures between eukaryotic and prokaryotic cells?
Eukaryotic cells have a more complex ultrastructure than prokaryotic cells. The term ultrastructure refers to the internal structure of cells. The cytoplasm of eukaryotic cells is divided up into membrane-bound compartments called organelles.
What is the cell surface (plasma) membrane?
All cells are surrounded by a cell surface membrane which separates the inside of cells from their surroundings. Cell surface membranes controls the exchange of materials between the internal cell environment and the external environment. The membrane is described as being partially permeable as it allows the passage of some substances but not others. The cell membrane is formed from a phospholipid bilayer and spans a diameter of around 10nm.
What is the nucleus, nuclear membrane, nuclear envelope, nuclear pores and nucleolus?
The nucleus is present in all eukaryotic cells and is a large organelle that is separated from the cytoplasm by a double membrane. The nucleus contains DNA, which is arranged into chromosomes. Chromosomes contain DNA and proteins which are collectively referred to as chromatin.
The nuclear membrane is known as the nuclear envelope and contains many pores. Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes and signalling molecules to move in.
The nucleus contains a region called the nucleolus which is the site of ribosome production.
What is the endoplasmic reticulum?
The endoplasmic reticulum (ER) is made up of a series of membranes that form flattened sacs within the cell cytoplasm. The ER is linked with the nuclear envelope. There are two types of ER: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
The rough endoplasmic reticulum (RER) contains continuous folds of membrane that are linked with the nuclear envelope. The surface of the RER is covered in ribosomes. The role of the RER is to process proteins that are produced on the ribosomes.
The smooth endoplasmic reticulum (SER) does not have any ribosomes on the surface. It is involved in the production of lipids, as of steroid hormones such as oestrogen and testosterone.
What is the Golgi body?
The Golgi body is often referred to as the Golgi apparatus or the Golgi complex. It consists of a series of flattened sacs of membrane. It can clearly be distinguished from the ER, as it is not connected to other membrane-bound compartments, and it has a distinctive ‘wifi symbol’ appearance. Its role is to modify proteins and package then into vesicles.
What is the mitochondria?
Mitochondria (singular mitochondrion) are relatively large organelles surrounded by a double membrane. They are smaller than the nucleus and chloroplasts but can be seen with a light microscope. The inner membrane is folded to form cristae which provides a large surface area for embedded proteins that are involved with aerobic respiration. Mitochondria are the site of aerobic respiration within eukaryotic cells. The mitochondrial matrix contains enzymes needed for aerobic respiration. Small, circular pieces of DNA, known as mitochondrial DNA, and ribosomes are also found in the matrix. This allows for the production of proteins required for respiration.
What are ribosomes?
Ribosomes are found in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells. Each ribosome is a complex of ribosomal RNA (rRNA) and proteins. 80s ribosomes are found in eukaryotic cells. Smaller, 70s ribosomes) are found in prokaryotes, mitochondria and chloroplasts. Ribosomes are the site of translation during protein synthesis. Ribosomes are formed in the nucleolus and are composed of almost equal amounts of RNA and protein.
What are vesicles?
Vesicles are small, membrane-bound sacs used by cells for transport and storage. They can be pinched off the ends of the Golgi body; these are known as Golgi vesicles. They can fuse with the cell surface membrane to allow exocytosis, or bud from the membrane during endocytosis.
What are lysosomes?
Lysosomes are specialised vesicles which contain hydrolytic enzymes which break down biological molecules such including waste materials such as worn-out organelles, engulfed pathogens during phagocytosis and cell debris during apoptosis (programmed cell death).
What are centrioles?
Centrioles are hollow fibres made of microtubules. Two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division. Centrioles are involved with the movement of chromosomes during cell division. Centrioles are not found in flowering plants or fungi.
What are microtubules?
Microtubules are hollow tubes made of tubulin protein. α and β tubulin proteins combine to form dimers, which are then joined into protofilaments. Thirteen protofilaments in a cylinder make a microtubule. Microtubules make up the cytoskeleton of the cell which provides support and movement of the cell.
What are cilia?
Cilia are hair-like projections made from microtubules. They can be found of the surface of some cells where they allow the movement of substance over the cell surface. E.g. ciliated epithelial cells in the airways waft mucus away from the lungs.
What are microvilli?
Microvilli are cell membrane projections that increase the surface area for absorption. Microvilli are found in parts of the body that carry out absorption e.g. the lining of the small intestine and the kidney tubules.
What are cell walls?
Cell walls are the outside cell surface membranes and offer structural support to some types of cell. Structural support is provided by the polysaccharide cellulose in plants and by the chitin in fungi. Cell walls are freely permeable and do not play a role in controlling the movement of substance into and out of cells.
What are chloroplasts?
Chloroplasts are larger than mitochondria and are also surrounded by a double membrane. Membrane-bound compartments called thylakoids stack together to form structures called grana. Grana are joined together by lamellae. Photosynthetic pigments such as chlorophyll are found in the membranes of the thylakoids, where their roles is to absorb light energy for photosynthesis. Chloroplasts contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis.
What is the plasmodesmata?
Plasmodesmata are the bridges of cytoplasm between neighbouring plant cells. This means that the cytoplasm of neighbouring plant cells is continuous which allows for substances to move easily between cells. E.g. sucrose can move easily from the surrounding cells into the phloem.
What are large permanent vacuoles?
Large permanent vacuoles are found in plant cells, where they store cell sap and provide additional structure to support cells. Vacuoles are sometimes found in animal cells, but these will be small and temporary. Vacuoles are surrounded by the tonoplast, which is a partially permeable membrane that separates the inner vacuole from the outer cellular cytoplasm.
Animal cell diagram
Plant cell diagram
What are some uses for ATP?
All organisms require a constant supply of energy to maintain their cells and stay alive. This energy is required in anabolic reactions to build larger molecules from smaller molecules, to move substances across the cell membrane in active transport, or to move substances within the cell and in animals’ energy is required for muscle contraction and in the conduction of nerve impulses.
Where is ATP produced?
ATP from respiration in the mitochondria is used to transfer energy in all energy-requiring processes in cells; this is why ATP is known as the universal energy currency. Energy is released from ATP when it is broken down due to ADP and inorganic phosphate. This process is reversed during respiration to make ATP and maintain a supply of energy.
Adenosine triphosphate (ATP) is a nucleotide. The monomers of DNA and RNA are also nucleotides.
What type of cells are bacteria cells?
Prokaryotic.
What are some features of prokaryotic cells compared to eukaryotic cells?
Their genetic material is free in the cytoplasm and is circular whereas eukaryotic genetic material is packaged as linear chromosomes in the nucleus.
Prokaryotes lack membrane-bound organelles which means that they do not have any internal structures surrounded by a membrane.
They are many times smaller than eukaryotic cells. Prokaryotic cells are usually 1-5μm in diameter while eukaryotic plant cells can be 10-100μm in diameter.
Their ribosomes are structurally smaller (70s) in comparison to those found in eukaryotic cells (80s).
Their cell walls are made of peptidoglycan rather than cellulose or chitin.
Prokaryotes are always unicellular, while eukaryotic animal and plant cells can function together in multicellular organisms.
Diagram of a bacterial cell
What are some differences between prokaryotes and eukaryotes?
What are viruses?
Viruses are non-cellular particles that infect living cells. Viruses are not cells, and they are not considered to be living organisms, so they are referred to as particles.
What are some structural features of viruses?
They are much smaller than prokaryotic cells, with a diameter of 20-300nm. Structurally, they have a nucleic acid core made of either DNA or RNA and a protein coat called a capsid. Some viruses have an outer layer called an envelope; this forms from the membrane phospholipids of the host cell in which they were produced. Viruses can only reproduce by infecting living cells and using their protein-building machinery to produce new viral particles. Viruses use attachment proteins on their surface to bind and infect their host cells.
