Cells Flashcards
What is a slide ?
A slide is a thin piece of glass used to hold objects which are examined under a microscope.
Most slides will already be made up for you. If you do get the chance to prepare your own slide, here’s what to do:
Plant cells ?
Peel a thin, transparent layer of epidermal cells from the inside of an onion.
Place cells on a microscope slide.
Add a drop of water or iodine (a chemical stain).
Lower a coverslip onto the onion cells using forceps or a mounted needle. This needs to be done gently to prevent trapping air bubbles.
Animal cells ?
Remove cells from the inside of your cheek using a cotton bud.
Smear the cotton bud onto a microscope slide.
Add a drop of methylene blue (a chemical stain).
Lower a coverslip onto the cheek cells using forceps or a mounted needle. This needs to be done gently to prevent trapping air bubbles.
Chemical stains are used to make some cell parts more obvious.
How to use aUsing a light microscope ?
Eyepiece
Objective lens
Stage
Focusing knob
Light source
When using a light microscope it’s important to start with the low power objective lens as the field of view will be wider, increasing the number of cells you are able to see.
This makes it easier to find what you’re looking for.
Then, ensuring the cells are in the middle of the field of view, rotate a higher powered lens into place and begin to focus to view the cells in more detail.
Extra care is needed here because the high-powered lens can become damaged as it’s very close to the slide.
Animal cells are made up of many different elements:
Structure Function
Nucleus Control centre of the cell. It contains the cell’s genetic information arranged in chromosomes.
Chromosomes Threadlike structure found in the nucleus. Made of DNA which contains the genetic information of the cell.
Cytoplasm Chemical reactions take place here.
Cell membrane A selectively permeable boundary surrounding the cell which allows some substances to enter and leave the cell while preventing others.
Nuclear membrane Surrounds nucleus.
Plant cells contain all of the elements which make up animal cells, but they also include:
Structure Function
Cellulose cell wall A rigid structure outside the cell membrane that provides support.
Large permanent vacuole Contains cell sap and when full pushes the cell membrane against the cell wall, providing support.
Chloroplasts Contain chlorophyll, a green pigment that traps light for photosynthesis.
Stem Cells ?
Stem cells are simple, unspecialised cells found in animals and plants that have the ability to divide to form cells of the same type. They can also differentiate into a variety of specialised cells.
Stem cells can be harvested from embryonic umbilical cord or adult bone marrow.
The use of stem cells in medicine is becoming more common. There are benefits and risks associated with their use in this field.
Benefits:
Treating leukaemia - chemotherapy and radiotherapy destroy white blood cells in the patient’s body, stopping their bone marrow producing new blood cells. A bone marrow transplant containing stem cells from a matching donor allows healthy blood cells to be made in the patient.
Risks:
Risk of infection from the environment (and the donor) as chemotherapy and radiotherapy leave the patient with no immune system.
Stem cells may divide in an uncontrolled manner leading to the formation of tumours or the development of unwanted cell types.
Transfer of viruses or diseases from other animals.
Some people have ethical issues with the use of embryonic stem cells and governments tend to control research in this area.
Specialisation cells
Organisms can be:
Single-celled - where all life processes are carried out by one cell.
Multi-celled - where cells differentiate and become specialised to carry out a particular function (e.g. red blood cells carry oxygen)
Specialised cells are organised. There are different levels of organisation:
Cells with the same structure and function are known as tissue (e.g. muscle tissue).
Several types of tissue that carry out a particular function is an organ (e.g. the heart organ contains muscle and nerve tissue).
Organs that work together to carry out a particular function are known as an organ system. (e.g. the circulatory system.
Why are chemical stains used?
It’s to make some cell parts more obvious.
Why should a low power objective lens be used first when viewing cells?
A low power objective lens should be used first when viewing cells as it has a wider field of view.
How is total magnification calculated?
It’s the eyepiece lens magnification multiplied by objective lens magnification.
Which of the following is found in plant cells but not in animal cells?
It’s chloroplast. Chloroplasts are tiny structures in plant cells where photosynthesis happens.
Which is the correct order of levels of organization in organisms, from least complex to most complex?
The correct order is cells -> tissues -> organs.
What is a tissue?
It’s a group of cells with similar structures working together.
