Topic 1-Cell biology (cell structure and cell division) Flashcards
What are all living things made from?
All living things are made of cells. Cells are the basic unit of all forms of life.
What two types of cells are there?
Cells can be either PROKARYOTIC or EUKARYOTIC.
What are the differences between eukaryotic cells and prokaryotic cells?
Eukaryotic cells are COMPLEX and include all animal and plant cells. Prokaryotic cells are SMALLER and SIMPLER, e.g. bacteria.
What are eukaryotes and a prokaryote?
EUKARYOTES are organisms that are made up of eukaryotic cells.
A PROKARYOTE is a prokaryotic cell (it is a single-celled organism).
What is the sub cellular structure of most animals?
- Animal cells are eukaryotic.
1) NUCLEUS- contains genetic material that controls the activities of the cell.
2) CYTOPLASM- a gel-like substance where most chemical reactions happen. It contains enzymes that control these reactions.
3) CELL MEMBRANE- holds the cell together and controls what goes in and out.
4) MITOCHONDRIA- these are where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work.
5) RIBOSOMES- these are where proteins are made in a cell.
What is the sub-cellular structure of most plant cells?
Plant cells usually have all the bits that animal cells have plus a few extra:
1) CELL WALL- a rigid structure made of cellulose. It supports and strengthens the cell. The cells of algae (e.g. seaweed) also have a rigid cell wall.
2) PERMANENT VACUOLE- contains cell sap, a weak solution of sugar and salts. This helps the cell remain turgid.
3) CHLOROPLASTS- these are where photosynthesis occurs, which makes food for the plant. They contain a green substance called chlorophyll, which absorbs the light needed for photosynthesis.
* The cells of algae (e.g. seaweed) also have a rigid cell wall and chloroplasts.
What is the structure of bacterial cells?
BACTERIAL cells are PROKARYOTIC. They are SMALLER than eukaryotes.
A bacterial cell has CYTOPLASM and a CELL MEMBRANE surrounded by a CELL WALL.
Bacterial cells don’t have a ‘true’ nucleus-instead they have a single circular strand of DNA that coats freely in the cytoplasm.
They may also contain one or more small rings of DNA called PLASMIDS.
Remember- bacteria don’t have chloroplasts or mitochondria.
What are plasmids?
-Plasmids are rings of DNA separate from the main DNA in the bacteria.
Each plasmid is made up of just a few genes that will control a few characteristics.
What can bacterial cells do to their DNA that animal and plant cells can’t?
-Bacteria are able to make copies of their plasmid and share it with other bacterial cells.
How can the replication and sharing of plasmids with other bacterial cells be an advantage?
This can be an advantage as the plasmid may have useful genes on it- if the plasmid has a gene for antibiotic resistance in it, and this is passed to another bacteria, the second bacteria will be resistant to the antibiotics too.
This is how antibiotic resistance has developed.
Are all cells identical?
In reality the structure of a cell varies according to what job it does.
What is microscopy?
Microscopy is the study of very small objects (such as cells) using an instrument called a microscope.
What do microscopes allow us to do?
How have microscopy techniques developed over time?
Microscopes let us see things that we can’t see with the naked eye.
Microscopy techniques we can use have developed over the years as technology and knowledge have improved.
How long have microscopes been in use for?
Microscopes have been in use for 350 years.
Early microscopes did not magnify to a great extent and scientists have worked hard to improve this.
What is resolution?
Resolution is the ability to distinguish two objects from one another.
What is magnification?
Magnification is the ability to enlarge an image.
What are two common types of microscopes?
The LIGHT microscope and the ELECTRON microscope.
How do light microscopes work?
-Light microscopes use light and lenses to form an imagoes a specimen and magnify it (make it look bigger). They let us see individual cells and large sub-cellular structures, like nuclei.
How do electron microscopes work?
Electron microscopes use electrons instead of light to form an image.
What are the features of a light microscope?
Advantages:
1) You can use living samples.
2) You can view samples in colour.
3) Much cheaper than electron microscopes.
4) Easier to carry/transport
Disadvantages:
1) Magnify up to 2 thousand times.
2) Light microscopes can only distinguish between points which are 200 nm apart.
What are the features of an electron microscope?
Advantages:
1) Can magnify up to 2 million times. (Higher magnification than light microscope).
2) Much higher resolving power/resolution of 0.2 nm, (better than a light microscope).Resolution is the ability to distinguish between two points, so a higher resolution gives a sharper image.
This means that it can be used to study cells in much finer detail. This has enabled biologists to see and understand many more sub-cellular structures, e.g. the internal structure of mitochondria and chloroplasts. They even let us see tinier things like ribosomes and plasmids.
Disadvantages:
1) You cannot use living samples.
2) The images are in black and white (pictures are often coloured in or dyed).
3) Cumbersome.
What is the formula to calculate the magnification of an image?
Note: image size and real size should have the same units. If they don’t you will have to convert them first.
magnification = size of image
___________
size of real object
or
magnification=
eye piece lens magnif x objective lens magnif
Remember it as: I
A M
How do you convert between cm to mm and micro metres to millimetres.
cm —> mm x 10
μm —> mm ÷ 1000
What is the first step to look at a specimen e.g. plant or animal cells under a light microscope?
First you must put the specimen on a microscope slide.
What is a slide?
A slide is a strip of clear glass or plastic onto which the specimen is mounted.
How do you prepare a slide to view onion cells?
Tip- sometimes you can place the specimen on the slide without it being suspended in liquid-it depends on what you’re looking at.
1) Add a DROP OF WATER to the middle of a clean slide.
2) Cut up an onion and separate it out into LAYERS. Use TWEEZERS to peel off some EPIDERMAL TISSUE from the bottom of one of the layers.
3) Using the tweezers, place the epidermal tissue into the WATER on the slide.
4) Add a drop of IODINE SOLUTION. Iodine solution is a STAIN. Stains are used to highlight objects in a cell by adding COLOUR to them.
5) Place a COVER SLIP (a square of thin, transparent plastic or glass) on top. To do this stand the cover slip UPRIGHT on the slide, NEXT TO the water droplet. Then carefully TILT and LOWER it so it covers the specimen. Try NOT to get any AIR BUBBLES under there- they’ll OBSTRUCT your view of the specimen.
Why are stains used when preparing a slide?
In light microscopes, the beam of light passes through the object being viewed. An image is produced because some parts of the object absorb more light than others. Sometimes the object being viewed is completely transparent, so the whole thing looks white because the light rays just pass straight through. To get around this, stains are used to highlight parts of the object.
Explain the steps involved to observe your prepared slide…
- Clip the SLIDE you’ve prepared onto the STAGE.
- Select the LOWEST-POWERED objective lens (i.e. the one that produces the lowest magnification).
- Use the COARSE ADJUSTMENT KNOB to move the stage up to just below the objective lens.
- Look down the EYEPIECE. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus.
- Adjust the FOCUS with the FINE ADJUSTMENT KNOB, until you get a CLEAR IMAGE of what’s on the slide.
- If you need to see the slide with GREATER MAGNIFICATION, swap to a HIGHER-POWERED OBJECTIVE LENS and refocus.
How do you draw your observations?
N.b. Students should be able to use estimations and explain when they should be used to judge the relative size or area of sub-cellular structures. Go to page 29 of cgp book to learn this!
1) Draw what you see under the microscope using a SHARP PENCIL.
2) Make sure your drawing takes up at LEAST HALF of the space available and that it is drawn with CLEAR, UNBROKEN LINES.
3) Your drawing should not include any COLOURING or SHADING.
4) If you are drawing CELLS, the SUB-CELLULAR STRUCTURES should be drawn in PROPORTION.
5) Remember to include a TITLE of what you were observing and write down the MAGNIFICATION that it was observed under.
6) LABEL the IMPORTANT FEATURES of your drawing, using STRAIGHT, UNCROSSED LINES.
What is a specialised cell?
A specialised cell is one that performs a specific function. Most cells in an organism are specialised. A cell’s structure help it to carry out its function (such as transporting a certain substance or executing a specific task).
While they have most of the same features as other cells, specialised cells have structural adaptations that help them do their jobs.
What is differentiation?
Differentiation is the process by which a cell CHANGES to become SPECIALISED for its job.
How do cells differentiate?
As cells change, they develop DIFFERENT SUB-CELLULAR STRUCTURES and turn into DIFFERENT TYPES OF CELLS. This allows them to carry out SPECIFIC FUNCTIONS.
When does differentiation occur in animal cells?
Most differentiation occurs as an organism DEVELOPS so most animal cells differentiate at an early stage.
Can animal cells differentiate at a later stage?
In MOST animal cells, the ability to differentiate is then LOST at an early stage, after they become specialised.
What is cell differentiation used for in mature animals?
The cells that differentiate in mature animals are mainly used for REPAIRING old or damaged cells and REPLACING CELLS, such as skin or blood.
When do plant cells differentiate?
Plant cells differentiate much later in their development.
Do plant cells lose their ability to differentiate?
Many types of plant cells retain the ability to differentiate throughout life.
What are undifferentiated cells called?
Some cells are undifferentiated cells- they’re called STEM CELLS.
How are nerve cells specialised for rapid signalling?
The function of nerve cells is to CARRY ELECTRICAL SIGNALS from one part of the body to another.
1) Has a long axon (which is the central nerve which forms the length of the neurone i.e. nerve fibre) this allows the nerve cell to carry electrical signals LONG DISTANCES.
Lots of dendrites (branched connections) anther ends CONNECT to other nerve cells and form a NETWORK throughout the body.
2) Nerve cells are very active so have lots of MITOCHONDRIA to release energy in aerobic respiration.
3) The nerve cell is covered with a fatty sheath, which insulates the nerve cell and speeds up the nerve impulse.
What is the function of a sperm cell?
The function of a sperm is basically to get the male DNA to the female DNA.
How are sperm cells specialised for reproduction?
1) The ACROSOME in the head contains enzymes which DIGEST through the egg cell membrane so that the sperm can penetrate an egg.
2) There are a lot of mitochondria in the cell to provide the energy needed to swim and fertilise the egg.
3) The flagellum (tail) enables the sperm to swim.
What is the function of a muscle cell?
The function of a muscle cell is to CONTRACT QUICKLY..
How are muscle cells specialised?
1) These cells are LONG (so that they have the space to CONTRACT).
2) They contain LOTS OF MITOCHONDRIA to generate the ENERGY needed for contraction.
3) Muscles store glucose in the form of glycogen. Glycogen is the storage compound of glucose. It is used when more energy is needed, and it breaks down to carry out respiration.
