Cell Biology 3 Flashcards
How do prokaryotic cells reproduce?
By simple cell division (binary fission).
What is Asexual reproduction?
Reproduction that only requires one parent. It results in the production of genetically identical offspring.
Up to how often can bacteria multiply?
As often as 20 minutes if they have enough nutrients and a suitable temperature.
How can bacteria be grown/cultured?
In a nutrient broth solution or as colonies on an agar gel plate.
What is required for investigating the action of disinfectants and antibodies?
Uncontaminated culture(s) of microorganisms.
What are the conditions affecting speed of bacterial division?
-Temperature
-Nutrient availability
-Moisture
-Oxygen
How do we calculate cross-sectional
areas of colonies or clear
areas around colonies?
using the formula πr²
How is the number of bacteria in a colony calculated?
2 to the power of the number of divisions
How do we work out the number of divisions of a bacterial colony?
Total time bacteria are producing cells ÷ mean division time.
(use the same unit of time!!)
What does nutrient broth or agar (‘media’) provide for bacteria in order to grow?
Carbohydrates
Nitrogen compounds
Vitamins and minerals
Why must petri dishes and culture media must be sterilised before use?
To kill any bacteria in the agar or petri dish and avoid growing other bacteria.
Why must the inoculating loops used to transfer microorganisms to an agar plate be sterilised/flamed?
The inoculating loop must be sterilised/flamed to kill any bacteria on the loop.
Why should the lid of the Petri dish be secured with adhesive tape?
To stop microorganisms from the air getting in.
Why should you only tape 3-4 points of a petri dish, not all the way around?
To allow oxygen in and prevent the growth of anaerobic bacteria.
In school laboratories, why should bacterial cultures should generally be incubated at 25°C?
To prevent the growth of harmful pathogens.
How do we write things in standard form?
e.g. 1.23 x 10³
What is the point of using a filter paper disc with distilled water on?
As an experimental control - it proves the paper does not affect bacterial growth and that any effect is due only to the disinfectants/antibiotics being tested.
What is an inoculating loop used for?
To transfer bacteria from a solution to agar.
What does the nucleus of a cell contain?
Chromosomes made of coiled up lengths of DNA molecules
How are chromosomes usually found in the body?
In pairs.
How many pairs of chromosomes do human cells have?
23 (46 altogether)
How do eukaryotic cells divide?
In a series of stages called the cell cycle.
What do genes control?
The development of different characteristics e.g. hair colour.
What are new cells needed for?
-Growth
-Development
-Repair
Growth and DNA replication step 1:
-The cell gets larger and produces more sub-cellular structures such as mitochondria and ribosomes
Mitosis:
-Chromosomes line up along the centre of the cell
-Cell fibres pull the two arms of each chromosome to opposite poles of the cell
Cytokinesis:
-Membranes form around each set of chromosomes. These become the nuclei of the two new cells (the nucleus has divided).
-The cytoplasm and cell membrane divide
-The cell has now produced two genetically identical ‘daughter cells’.
-The DNA is also identical to the parent cell.
What are the stages of the cell cycle?
-Growth and DNA replication
-Mitosis
-Cytokinesis
Briefly explain what happens during the Cell cycle.
A cell’s genetic material is doubled and then divided into two identical cells.
Where does asexual reproduction occur?
Predominantly in plants.
What are the first 2 steps in binary fission?
1- The bacterial cell grows and replicates its genetic material (a circular strand of DNA and plasmids).
2- The two circular strands of DNA move to opposite poles of the cell.
What are the third and fourth steps in binary fission?
3- The cytoplasm begins to divide and a new cell wall forms down the centre of the cell
4- The cytoplasm divides and two ‘daughter cells’ are produced.
What is the final step in binary fission? (hint - daughter cells)
5- Each daughter cell has one copy of the circular DNA, but a variable number of plasmid(s).
What do we need to make sure is correct in calculations?
Units!
Why do bacteria need carbohydrates?
For respiration, which releases the energy that the cell needs to grow and divide.
Why do bacteria need nitrogen compounds?
For protein synthesis
How do we sterilise inoculating loops?
By passing them through a flame (flaming them).
Growth and DNA replication step 2:
-The cell duplicates its DNA so there’s one copy for each new cell.
-The DNA then condenses to form X-shaped chromosomes.
-Each ‘arm’ of the chromosome is an exact duplicate of the other.
What indicates the most effective antibiotic/antiseptic tested? (rp)
The largest zone of inhibition and therefore the most bacteria killed.
Potential sources of contamination
-Skin
-Air
-Soil
-Water
For investigations into antibiotics to be useful, the cultures must be what?
pure
How are solutions and agar sterilised?
They must be boiled
Why should the dish should be stored upside down? (rp)
To prevent condensation forming on the lid and then dripping onto the agar, contaminating the solution.
Where are chromosomes found?
Chromosomes are found in cell nuclei.
What do chromosomes contain? (in the dna molecules)
Many different genes that encode (produce) many different proteins.
Mitosis ensures that both daughter cells have the same chromosomes as each other and the parent cell. When is this important?
For processes that require identical cells to be produced e.g. the growth and repair of tissues and asexual reproduction.
Why must we only lift the lid of the petri dish a little?
Fewer bacteria will enter.
