Topic 1-Cell Biology Flashcards
What does a nucleus do?
- Contains the genetic DNA of the organism
- Enclosed in a nuclear membrane
- Controls and regulates the activities of the cell
What is cytoplasm?
- Liquid substance in which chemical reactions occur
- Contains enzymes (biological catalysts, i.e. proteins that speed up the rate of reaction)
- Organelles are found in it
What is the cell membrane?
-Controls what enters and leaves the cell
What do ribosomes do?
- Where protein synthesis occurs
- Found on a structure called the rough endoplasmic reticulum
What do chloroplasts do?
- Where photosynthesis takes place, providing food for the plant
- Contains chlorophyll pigment (which makes it green) which harvests the light needed for photosynthesis
What is a permanent vacuole?
- Contains cell sap
- Found within the cytoplasm
- Improves cell’s rigidity
What is a cell wall?
- Made from cellulose
- Provides strength to the cell
What are plasmids?
Small rings of DNA
What happens when cells differentiate?
-They gain sub-cellular structures in order for it to be suited to its role
How are sperm cells specialised to carry the male’s DNA to the egg cell for successful reproduction?
- Streamlined head and long tail to aid swimming
- Many mitochondria (where respiration happens) which supply the energy to allow the cell to move
- The acrosome (top of the head) has digestive enzymes which break down the outer layers of membrane of the egg cell
How are nerve cells specialised to transmit electrical signals quickly from one place in the body to another?
- The axon is long, enabling the impulses to be carried along long distances
- Having lots of extensions from the cell body (dendrites) means branched connections can form with other nerve cells
- Nerve endings have many mitochondria which supply the energy to make special transmitter chemicals called neurotransmitters.
- These allow the impulse to be passed from one cell to another
How are muscle cells specialised to contract quickly to move bones or to simply squeeze, therefore causing movement?
- Special proteins (myosin and actin) slide over each other, causing the muscle to contract
- Lots of mitochondria to provide energy from respiration for contraction
- They can store a chemical called glycogen that is used in respiration by mitochondria
How are root hair cells specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of roots?
- Large surface area due to root hairs-more water can move in
- Large permanent vacuole affects the speed of movement of water from the soil to the cell
- Mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell
How are xylem cells specialised to transport water and mineral ions up the plant from the roots to the shoots?
- Upon formation, a chemical called lignin is deposited which causes the cells to die. They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through
- Lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water
How are phloem cells specialised to carry the products of photosynthesis (food) to all parts of the plants?
- Cells walls of each cell 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 of the companion cells
How do you figure out the size of an object?
Size of image/magnification = size of object
What is a nutrient broth solution?
It involves making a suspension of bacteria to be grown and mixing with sterile nutrient broth (the culture medium).
In a nutrient broth, why must you stoppper the flask with cotton wool?
To prevent air from contaminating it
When working with a nutrient broth, why is it important to shake the flask regularly?
To provide oxygen for the growing bacteria
How do you grow microorganisms on an agar gel plate?
The agar acts as the culture medium, and the bacteria grown on it form colonies on the surface
- Hot sterilised agar jelly is poured into sterilised petri dish (cool and set)
- Inoculating loops are dipped in solution of microorganism and spread over agar evenly
- Lid is taped on and incubated so microorganisms can grow
Why must petri dishes and culture media be sterilised before use, which is often done by an autoclave (an oven) or UV light?
They are likely to be contaminated with other microorganisms. These could be harmless but will compete with the desired bacteria for nutrients and space, or they could be harmful (eg. a mutation), potentially creating a new pathogen
Why must inoculating loops be sterilised by passing them through a flame?
This kills unwanted microorganisms
Why should the lid of the Petri dish be sealed, but not completely, with tape
Sealing stops airborne organisms from contaminating the culture, but it should not be sealed all the way around as this would result in harmful anaerobic bacteria growing (due to no oxygen)
Why should the Petri dish be stored upside down?
This is to prevent condensation from the lid landing on the agar surface and disrupting growth
Why should the culture be incubated at 25 degrees?
If it were to be incubated at a higher temperature, nearer 37 degrees (body temp), it would be more likely that bacteria that could be harmful to humans would be able to grow as this is their optimum temperature. At lower temperatures, colonies of such bacteria would not be able to grow
How do you test the effectiveness of antibiotics against the growth of a certain bacteria?
Soak the paper disks in different types/concentrations of antibiotics and place on an agar plate evenly spread with bacteria. One disc should be a control, soaked in sterile water. There should be no death of bacteria with this disk (showing the change in inhibition zone size is purely due to the antibiotics)
How many pairs of chromosomes does each cell of the body have?
23 pairs, 46 chromosomes in total
What are the 3 stages of the cell cycle?
Interphase
Mitosis
Cytokinesis
What happens during Interphase?
In this stage the cell grows, organelles grow and increase in number, the synthesis of proteins occurs, DNA is replicated and energy stores are increased
What happens during Mitosis?
The chromosomes line up at the equator of the cell and cell fibres pull each chromosome of the ‘X’’ to either side of the cell
What happens during Cytokinesis?
Two identical daughter cells form when the cytoplasm and cell membranes divide
Why is mitosis important in multicellular organisms?
Important in their growth and development and when replacing damaged cells
What are embryonic stem cells?
- Form when an egg and sperm cell fuse to form a zygote
- They can differentiate into any type of cell in the body
- Scientists can clone these cells (though culturing them) and direct them to almost any cell in the body
How could embryonic stem cells be used?
- To replace insulin-producing cells in those suffering from diabetes
- New neural cells for diseases such as Alzheimer’s
- Nerve cells for those paralysed with spinal cord injuries
What are adult stem cells?
If found in bone marrow, they can form many types of cells including blood cells
What are meristems in plants?
- Found in root and shoot tips
- They can differentiate into any type of plant and have this ability throughout the life of the plant
- They can be used to make clones of the plant-this may be necessary if the parent plant has certain desirable features (eg disease resistance), for research or to save a rare plant from extinction
What is therapeutic cloning?
- Involves an embryo being produced with the same genes as the patient
- Embryo produced could then be harvested to obtain the embryonic stem cells
What are some of the benefits of therapeutic cloning?
- The embryonic stem cells can be grown into any cells the patient needed, such as new tissues or organs
- They would not be rejected as they would have the exact same genetic make-up as the individual
What are some of the benefits of research with stem cells?
- Can be used to replace damaged or diseased body parts
- Unwanted embryos from fertility clinics could be used as they would otherwise be discarded
- Research into the process of differentiation
What are some of the problems with stem cell research?
We do not completely understand the process of differentiation, so it is hard to control stem cells to form the cells we desire
- Removal of stem cells results in destruction of the embryo
- People may have religious or ethical objections as it is seen as interference with the natural process of reproduction
- If stem cells are contaminated with a virus, an infection can be transferred to the individual
- Money and time could be better spent into other areas of medicine
What is the definition of diffusion?
The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration
Where does diffusion take place in the body?
- Oxygen moves through the membranes of structure in the lung called alveoli into the red blood cells, and is carried to cells across the body for respiration.
- Carbon dioxide (waste product of respiration) moves from the red blood cells into the lungs to be exhaled. This is called gas exchange
- Urea moves from liver cells into blood plasma to be transported to the kidney for excretion
How does the concentration gradient affect the rate of diffusion?
The greater the difference in concentration, the faster the rate of diffusion. This is because more particles are randomly moving down the gradient than are moving against it
How does temperature affect the rate of diffusion?
The greater the temperature, the greater the movement of particles, resulting in more collisions and therefore a faster rate of diffusion
How does surface area of the membrane affect the rate of diffusion?
The greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion
How do single-celled organisms use diffusion?
- To transport molecules into their body from the air because they have a relatively large SA:V ratio
- Due to their low metabolic demands, diffusion across the surface of the organism is sufficient enough to meet its needs
How are lungs adapted for their job?
- They have a large surface area created by alveoli (more surface for the particles to move through)
- The alveoli walls are extremely thin (shorter diffusion distance)
- Concentration gradient is always steep due to the constant supply of oxygen from lungs
How is the small intestine adapted for its job?
- They have villi
- It has a large surface area due to the large number or villi
- Villi also have a single layer of surface cell
How are gills adapted for their job?
-They contain lamellae which increase the surface area
How are the roots of plants adapted to take up water and mineral ions?
-Root hair cells with large surface areas
How does having a thin membrane affect the rate of diffusion?
-Provides short diffusion pathway, allowing the process to occur faster
What the definition of osmosis?
The movement of water from a less concentrated solution to a more concentrated solution
What does ‘isotonic’ mean?
If the concentration of sugar in external solution is the same as the internal, there will be no movement and the solution is the same as internal
What does ‘hypertonic’ mean?
If the concentration of sugar in external solution is higher than the internal, water moves out, and the solution is said to be hypertonic
What does ‘hypotonic’ mean?
If the concentration of sugar in external solution is lower than the internal, water moves in and the solution is said to be hypotonic to the cell
What is the definition of active transport?
It is the movement of particles from an area where they are in lower concentration to an area where they are in higher concentration- against their concentration gradient (not passive)
How is active transport used in root hairs?
- They take up water and mineral ions (for healthy growth) from the soil
- Mineral ions are usually in higher concentrations in the cells, meaning diffusion cannot take place
- This requires energy from respiration to work
How is active transport used in the gut?
- Substances such as glucose and amino acids from your food have to move from your gut into your bloodstream
- Sometimes there can be a lower concentration of sugar molecules in the gut than the blood, meaning diffusion cannot take place
- Active transport is requires to move sugar to the blood against its concentration gradient
How do plant leaves and stems remain rigid?
Turgor pressure- water moves in by osmosis causing the vacuole to swell and the cytoplasm to press against the cell wall
What is the magnification of an electron microscope?
x2,000,000
resolving 10nm and 0.2nm
Define magnification
The number of times bigger an image appears compared to the size of the real object
Define resolution
The smallest distance between two objects that can be distinguished
How does a light microscope work?
The objective lense produces a magnified image of a specimen, which is then magnified and directed into the eye by the eyepiece lens, allowing the specimen to be observed
It is usually illuminated from underneath
What are the advantages of light microscopes?
Inexpensive
Easy to use
Portable
Observe both dead and living specimens
What is the disadvantage of light microscopes?
Limited resolution
How does an electron microscope work?
It uses a beam of electrons which are focused using magnets. The electrons hit a fluorescent screen which emits visible light, producing an image of the specimen
What are the two types of electron microscope?
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
What is the advantage of electron microscopes?
Greater magnification and resolution
Why do electron microscopes have a greater magnification and resolution?
They use a beam of electrons which has a shorter wavelength than photons of light
How have electron microscopes enabled scientists to develop their understanding of cells?
- Allow small sub-cellular structures (eg mitochondria, ribosomes) to be observed in detail
- Enable scientists to develop more accurate explanations about how cell structure relates to function
What are the disadvantages of electron microscopes?
- Expensive
- Large so less portable
- Require training to use
- Only dead specimens can be observed
How can magnification be calculated?
Magnification=size of image/size of real object
How do bacteria multiply?
Binary fission
How often do bacteria multiply?
Once every 20 minutes if enough nutrients are available and the temperature is suitable
State 2 ways in which bacteria can be grown
- Nutrient broth solution
- Colonies on an agar gel plate
What nutrients make up a nutrient broth solution?
All nutrients required for bacteria to grow including nitrogen for protein synthesis, carbohydrates for energy and other minerals
What are uncontaminated cultures of microorganisms needed for?
-Investigating disinfectant and antibiotic action
Describe the preparation of an uncontaminated culture using aseptic technique
- Use pre-sterilised plastic Petri dishes or sterilise glass Petri dishes and agar gel before using with an autoclave
- Pour the sterile agar gel into the Petri dish and allow time to set
- Sterilise the inoculation loop by passing it through a Bunsen burner flame
- Dip the inoculating loop into the solution of microorganisms and make streaks with the loop on the surface of the agar
- Put the lid on the Petri dish and secure it with tape. Label accordingly then turn and store upside down
- Incubate the culture at 25 degrees Celsius (if in schools)
What do mitochondria do?
It is where aerobic respiration reactions occur, providing energy for the cell
Name two pieces of laboratory equipment the student could have used to prepare cells to view using a microscope
Coverslip
Slide
Stain
Needle
What is the function of the focus wheel?
It is used to focus the image
The student tried to look at the cells using a microscope
Suggest one reason why the student could not see any cells when looking through part A
Stage was not high enough
Wrong lens
Not in focus
No light
Objective lens not aligned
Red blood cells are specialised animal cells
Compare the structure of a red blood cell with the structure of a plant cell
PC has cell wall/chloroplasts/vacuole
RBC has no cell wall/chloroplasts/vacuole
RBC and PC both has cell membranes and cytoplasm
PC has nucleus
RBC has no nucleus. It is a specialised cell which has a biconcave shape
PC has ribosomes and mitochondria
When placed into a beaker of water:
- a red blood cell bursts
- a plant cell does not burst
Explain why the red blood cell bursts but the plant cell does not burst
Plant cells have a cell wall made from cellulose
Animal cells only have cell membrane
It is also due to osmosis
Describe two aseptic techniques the student should have used when carrying out an experiment to investigate the effectiveness of three different antibiotics
- Sterilising petri dish or agar gel
- Sterilise the work surface
- Sterilise inoculating loop
- Only lift lid minimal amount
- Incubate at 25 (degrees Celsius)
Energy is released in respiration
Give two uses of the energy released in respiration
Chemical respiration
Movement
Active transport
Cell division
Describe two differences between aerobic and anaerobic respiration in humans
Aerobic respiration releases more energy than anaerobic respiration
Aerobic releases CO2 and H2O but anaerobic respiration releases lactic acid
What are the two products of anaerobic respiration in plant cells
Carbon dioxide
Ethanol
