Topic 1 Cells Flashcards
Why does a bacterial cell lack a true nucleus?
Instead of it containing chromosomes, the DNA is arranged in a single strand in the cytoplasm
What are plasmids? (In the bacterial cell)
Small rings of DNA
Cell membrane
Selectively permeable boundary surrounding the cell which allows some substances to enter and leave while preventing others
Cytoplasm
Chemical reactions take place here
Nuclear membrane
Surrounds nucleus
Nucleus
Control centre. Contains cellβs genetic information arranged in chromosomes
Mitochondria
Site of cell respiration. Very abundant in cells which need a lot of energy eg muscle cells
Cellulose cell wall
Rigid structure outside the cell membrane that provides support
Vacuole
Contain cell sap and when full pushes the cell membrane against the cell wall, providing support
Chloroplast
Contains chlorophyll - a green pigment that traps light for photosynthesis
Chlorophyll
Absorbs light for photosynthesis
How do you prepare an onion cell slide?
- Use forceps to peel off a layer of onion epidermis
- This single layer allows light through
- Place a drop of iodine on top of the onion to stain the structures
- Use a mounted needle to place cover slip on (so no bubbles)
What is the purpose of the iodine and methylene blue on your temporary mounts?
To act as a stain and allow the structures in the cell to be seen
Why must the onion tissue used be one cell thick?
To allow enough light to come through the specimen. If there was more than one layer it would be difficult to see the cells
Why is it important to only use the fine focus when viewing at high power?
To avoid crashing the lens into the slide and damaging it
What happens to the area of the specimen you can see as you increase magnification?
The area you see will decrease as you increase magnification
Properties of the low power objective lens
FOV is wider - there are more cells in less detail
Properties of the high power objective lens
FOV is smaller - there are fewer cells in more detail
How do you calculate total magnification?
Eyepiece magnification (x10) x objective lens magnification
What is the total magnification if the objective lens is x20?
10 x 20 =200
What is the total magnification if the objective lens was x100?
10 x 100 =1,000
How do you calculate magnification, image size or actual size? (IAM)
I = A X M
A = I / M
M = I / A
How do you convert micrometers into millimetres?
/1000
How do you convert millimetres into micrometers?
X1000
Unit of measurement for micrometers
ΞΌm
How do you use IAM when there is a scale bar?
Treat the scale bar as the ACTUAL SIZE
Properties of electron microscopes
Pass beams of electrons through a specimen and have a much greater resolution. They allow us to clearly see inside the parts of the cell eg chloroplasts or mitochondria
What is resolution?
The ability to see detail in an image
What substances need to enter the cell?
Oxygen, water, dissolved food molecules and mineral ions
What substances need to pass out of the cell?
Carbon dioxide and nitrogen wastes
What is diffusion?
Random movement of a substance from a region of high concentration to a region of low concentration
What is an example of diffusion?
Oxygen moves from a high concentration in the lungs to low concentration in the blood
Where does diffusion happen?
Across the cell membrane which is selectively permeable (allows some things through, stops others)
What is diffusion rate affected by?
Concentration gradient, temperature and surface area
What is concentration gradient?
The difference in the high/low concentrations
Why does temperature affect rate of diffusion?
Higher temperature gives particles more kinetic energy
Why does surface area affect rate of diffusion?
The larger the area where diffusion can happen the more diffusion rate increases
Why are single celled organisms small?
They have a large surface area compared to their volume. Since their needs can be met purely by diffusion it has to be small enough to do this. A larger cell has a smaller surface area compared to its volumeβs needs. If there isnβt enough area for the cell to survive purely on diffusion, it will die.
What are Unicellular organisms?
Single called organisms
What are multicellular organisms?
Made up of lots of cells
Does diffusion provide enough for unicellular organisms?
Yes as distances are short - they have a large surface area
Does diffusion provide enough for multicellular organisms?
No as the distances are to great - smaller surface area
How does a multicellular organism provide for itself?
It develops gas exchange organs (eg lungs) which have a greatly increased surface area. They also need a transport system (eg circulatory/respiratory) to deliver materials to/from exchange surfaces
How many cells are used for the processes carried out in unicellular organisms?
They are carried it by one cell
How are processes carried out in multicellular organisms?
Their cells differentiate and are specialised. They are then organised into groups eg tissue, organs, organ systems etc
Different groups of cells
Cells - tissues - organs - organ systems - organisms
Function and main organs of the respiratory system
To move air into the body and to remove carbon dioxide. Main organs are lungs, throat, mouth etc
Functions and main organs of the digestive system
Digest/absorb food, remove waste. Main organs include mouth, stomach, small/large intestine
What is a stem cell?
Simple, unspecialised cells that. Have the ability to divide into smaller cells of the same type. They can also differentiate into a variety of specialised cells
Where can stem cells be harvested in humans?
Embryoβs, umbilical cord or adult bone marrow
Difference between embryonic and adult stem cells
Embryonic can change, adult cant
What type of cells can bone marrow stem cells only turn into?
Blood cells
Where can stem cells be harvested from in plants?
Meristems
What are meristems?
Apical growing points
Where are meristems found?
End of shoots and roots
Are stem cells stuck with their specialisation? How can this benefit science?
No, they can be reversed under certain conditions. This means scientists can produce large numbers of genetically identical plants by cloning
Benefits of using stem cells in medicine
Treating leukaemia- chemotherapy/ radiotherapy destroys and stops the production of new blood cells. A matching donorβs stem cels allows new, healthy blood cells to be made in the patient
Risks of using stem cells in medicine
Infection - radiotherapy and chemotherapy leaves patient with no white blood cells and therefore no immune system
Risk of uncontrollable division leading to tumours/unwanted cell types
Transfer of viruses/diseases
What is peer review in medicine?
New research is validated or rejected by other experts in the same field to prevent spread of misinformation
Ethical issues relating to stem cells
Destruction of potential human life, some religions are opposed to it, βplaying Godβ, human rights issues
