Topic 1: Key Concepts in Biology Flashcards
MAGNIFICATION EQUATION
magnification= image size/real size M=I/A
TOTAL MAGNIFICIATION FORMULA
total magnification= eyepiece lens magnification x objective lens magnification
MICROSCOPE PRACTICAL:
1) Take a thin slice of your specimen.
2) Take a clean slide and use a pipette to put one drop of water in the middle of it- this will secure the specimen in place, and use tweezers to place your specimen on the slide.
3) Add a drop of stain (iodine) if your specimen is completely transparent or colourless- this makes the specimen easier to see ( different stains highlight different structures within cells, e.g. methylene blue stains DNA.
4) Place a cover slip at one end of the specimen, holding it at an angle with a mounted needle and carefully lower it onto the slide. Press it down gently so that no air bubbles are trapped under it. Then clip the slide onto the stage.
5) Select the lowest-powered objective lens.
6) Use the coarse adjustment knob to move the stage up so that the slide is underneath the objective lens. Then, looking down the eyepiece, move the stage downwards until the specimen is nearly in focus.
7) Then adjust the focus with the fine adjustment knob, until you get a clear image. Then, position a clear ruler on the stage and use it to measure the diameter of the circular area visible- your field of view.
- Measuring your FOV allows you to estimate the size of your specimen.
8) If you need to see your specimen with greater magnification, swap to a higher-power objective lens, refocus and recalculate your FOV accordingly.
- ( e.g. if your FOV was 5mm then you swap to a lens that is 10 times more powerful, your FOV will now be 5mm/10= 0.5mm)
Discoveries of the microscopes:
- The discovery of the electron microscope has allowed us to view many organelles more clearly- especially very small structures such as ribosomes. - TEMs have been used to discover viruses such as poliovirus, smallpox and Ebola.
- This is useful as viruses are much smaller than bacteria and are very hard to identify using a standard light microscope.
- Electron microscopes are also used to examine proteins in much greater detail than can be achieved with a light microscope which has led to many important scientific discoveries.
Information about electron microscopes:
- They were invented in the 1930s.
- They use a beam of electrons through the specimen.
- They have a higher magnification and resolution that enabled scientists to view deep inside sub-cellular structures, such as mitochondria, ribosomes, chloroplasts and plasmids.
- There are two types: a scanning electron microscope that create 3D images ( at a slightly lower magnification) and a transmission electron microscope which creates 2D images detailing organelles.
- They have a magnification up to 2,000,000x and resolving power of 10nm (SEM) and 0.2nm (TEM)
Information about light electrons:
- They were invented in 1590.
- They work by passing lights through the specimen.
- Approximately, a maximum magnification of 2000x and a resolving power of 200nm. The lower the resolution power, the more detail is seen.
- It is used to view tissues, cells and large sub- cellular structures.
What does resolution mean?
Resolution means how well a microscope distinguishes between two points that are close together. A higher resolution means that the image can be seen more clearly and in more detail.
How are phloem cells adapted to their function?
The phloem cells are specialised to carry the products of photosynthesis to all parts of the plants.
Cell walls of each form structures called sieve plates when they break down, allowing the movement of substances from cell to cell.
Despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria.
How are xylem cells adapted to their functions?
Xylem cells are specialised to transport water and mineral ions up the plant from the roots to shoot. They consists of dead cells.
They lose their end walls so the xylem forms a continuous, hollow tube.
They become strengthened by a substance called lignin. Lignin gives strength and support to the plant. Lignified cells are called wood.
Transport in the xylem is a physical process. It does not require energy.
How are root hair cells adapted to their functions?
The root hairs are where most water absorption happens. They are long and thin so they can penetrate between soil particles and they have a large surface area for absorption of water.
They have a large surface area due to root hairs, meaning more water can move in.
The large permanent vacuole affects the speed of movement of water. They have large vacuoles to absorb water quickly and transport it to the next cells. The vacuoles have salts, which speed up water absorption from soil water.
The mitochondria provides energy from respiration for the active transport of mineral ions into the root hair cell.
How is the ciliated epithelial cell adapted to its function?
The function of these cells is to move substances/fluid over the epithelial surface in structures such as the trachea, bronchial tubes, and nasal cavities.
Stomach - cilia beat to move bacteria trapped by sticky mucus down to the stomach, where they are killed by the stomach acid.
Lining of the airways contain lots of ciliated epithelial cells, help to move mucus up to the throat so it can be swallowed and doesn’t reach the lungs.
Cilia- beat to move substances in one direction, along the surface of the tissue
How is the sperm cell adapted to its function?
The function of the sperm cell is to carry the male’s DNA to the egg cell for successful reproduction.
Long Tail- has a long tail so it can swim to the egg
Mitochondria- in the middle section to provide the energy (from respiration) needed to swim the distance to the egg.
Acrosome- it has digestive enzymes which break down the outer layers of the egg cell’s membrane.
Nucleus- it has a haploid nucleus, contains a single set of chromosomes.
How are egg cells related to their functions?
The main function of an egg are to accept a single sperm, carry the female DNA and to nourish the developing embryo in the early stages.
Cytoplasm- contains nutrients to feed the embryo
Nucleus- has a haploid nucleus, contains a single set of chromosomes
Cell Membrane- straight after fertilisation, its membrane changes structure to sop any more sperm getting in, This makes sure the offspring end up with the right amount of DNA.
Mitochondria- provides an energy source for the developing embryo
What is a haploid and diploid?
A haploid describes a cell that has only one set of chromosomes- egg, sperm.
A diploid describes a cell that has two sets of chromosomes- skin cells, muscle cells
What happens in sexual reproduction?
The nucleus of an egg cell fuses with the nucleus of a sperm cell to create a fertilised egg, which then develops into an embryo.