Biology - Topic 1 - Cell Biology

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  • Created by: hannah.o
  • Created on: 15-02-18 16:38
What are eukaryotic cells?
Eukaryotic cells are complex and include all animal and plant cells. Eukaryotes are organisms that are made up of eukaryotic cells.
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What are prokaryotic cells?
Prokaryotic cells are smaller and simpler, e.g. bacteria. A prokaryote is a prokaryotic cell (single-celled organism).
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What are the different parts of a cell called?
Subcellular structures.
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What is the nucleus?
Contains genetic material that controls the activities of the cell.
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What is the cytoplasm?
Gel-like substance where most of the chemical reactions happen. It contains enzymes that control these chemical reactions.
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What is the cell membrane?
Holds the cell together and control what goes in and out.
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What is the mitochondria?
These are where most of the reactions for aerobic respiration take place. Respiration transfers energy that the cell needs to work.
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What are the ribosomes?
These are where proteins are made in the cell.
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What is the rigid cell wall?
Made of cellulose. It supports the cell and strengthens it.
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What is the permanent vacuole?
Contains cell sap, a weak solution of sugar and salts.
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What are the 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?
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How do light microscopes work?
Light microscopes use light and lenses to form an image of a specimen and magnify it. They let us see individual cells and large subcellular structures, like nuclei.
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How do electron microscopes work?
Electron microscopes use electrons not light to form an image. They have a much higher magnification than light microscopes. They also have a higher resolution. They let us see smaller things, like mitochondria, chloroplasts, ribosomes and plasmids.
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What is resolution?
The ability to distinguish between 2 points, so a higher resolution gives a sharper image.
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What is the formula for magnification?
Magnification = image size / real size
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How do you prepare a slide to view onion cells?(2)
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
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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 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 as these will obstruct your view of the specimen.
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How do you use a light microscope?
1) Clip the prepared slide onto the stage. 2) Select the lowest-powered objective lens. 3) Use the coarse adjustment knob to move the stage up to just below the objective lens. 4) Look down the eyepiece. Use the coarse adjustment knob to move the
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stage downwards until image is roughly in focus. 5) Adjust focus with fine adjustment knob, until you get a clear image of the slide. 6) If you need to see the slide with greater magnification, swap to a high-powered objective lens and refocus.
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What is differentiation?
Differentiation is the process by which a cell changes to become specialised for its job.
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What are undifferentiated cells called?
Stem cells.
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What are sperm cells specialised for?
Reproduction
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What is the function of a sperm cell?
To get male DNA to female DNA. It has a long tail and a streamlined head to help it swim to the egg. There are a lot of mitochondria in the cell to provide the energy needed. It also carrier enzymes in its head to digest through egg cell membrane.
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What are nerve cells specialised for?
Rapid signalling
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What is the function of a nerve cell?
To carry electrical signals from one part of the body to another. These cells are long (to cover more distance) and have branched connections at their ends to connect to other nerve cells and form a network throughout the body.
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What are muscle cells specialised for?
Contraction
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What is the function of a muscle cell?
To contract quickly. These cells are long (so that they have space to contract) and contain lots of mitochondria to generate the energy needed for contraction.
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What are root hair cells specialised for?
Absorbing water and minerals.
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What is the function of a root hair cell?
They are cells on the surface of plant roots, which grow into long 'hairs' that stick out into the soil. This gives the plant a big surface area for absorbing water and mineral ions from the soil.
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What are phloem and xylem cells specialised for?
Transporting substances.
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What is the function of phloem and xylem cells?
They form phloem and xylem tubes, which transport substances such as food and water around plants. To form the tubes, the cells are long and joined end to end. Xylem cells are hollow in the centre and phloem cells have very few subcellular structures
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Where is your genetic material kept and how?
It is in the nucleus in the form of chromosomes.
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What are chromosomes?
Chromosomes are coiled up lengths of DNA molecules. Each chromosome carries a large number of genes. Different genes control the development of different characteristics.
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How many pairs of chromosomes does a human cell have?
23 pairs - 46 chromosomes
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What is the cell cycle?
Where body cells in multicellular organisms divide to produce new cells as part of a series of stages.
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What is the stage of the cell cycle when the cell divides called?
Mitosis
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What are the two main stages if the cell cycle?
Growth & DNA replication and Mitosis.
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What does the cell cycle look like?
.
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What happens in the growth and DNA replication stage?
In a cell that's not dividing, the DNA is all spread out in long strings. Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes. It then duplicates its DNA - so there's one copy
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for each new cell. The DNA is copied and forms X-shaped chromosomes. Each 'arm' of the chromosome is an exact duplicate of the other.
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What happens in the stage mitosis?
After its contents and DNA have been copied, mitosis can happen... The chromosomes line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell. Membranes form around each of the
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sets of chromosomes. These become the nuclei of the two new cells - the nucleus has divided. Lastly, the cytoplasm and cell membrane divide. The cell has now produced two new daughter cells, which contains exactly the same DNA - they're identical.
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How do prokaryotic cells replicate?
By binary fission.
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What happens in binary fission?
The circular DNA and plasmid(s) replicate. The cell gets bigger and circular DNA strands move to opposite 'poles' of the cell. The cytoplasm begins to divide and new cell walls begin to form. The cytoplasm divides and two daughter cells are produced.
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How do you grow bacteria in a lab? (2)
1) Bacteria are grown (cultured) in a 'culture medium', which contains the carbohydrates, minerals, proteins and vitamins they need to grow. 2) The culture medium used can be a nutrient broth solution or solid agar jelly. 3) Bacteria grown on agar
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'plates' will form visible colonies on the surface of the jelly, or will spread out to given an even covering of bacteria. 4) In school labs, cultures of microorganisms are not kept above 25'C, because
harmful pathogens are more likely to grow above this temperature. 5) In industrial conditions, cultures are incubated at higher temperatures so they can grow a lot faster.
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How do you make an agar plate?
Hot agar jelly is poured into shallow round plastic dishes called Petri dishes. When the jelly's cooled and set, inoculating loops can be used to transfer microorganisms to the culture medium. Or, a sterile dropping pipette and spreader can be used
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to get an even covering of bacteria. The microorganisms then multiply.
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How do you test the action of antibiotics on cultures of bacteria? (3)
1) Place paper discs soaked in different types (or concentrations) of antibiotics on an agar plate that has an even covering of bacteria. Leave space between the discs. 2) The antibiotic should diffuse into the agar jelly. Antibiotic-resistant will
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continue to grow on the agar around the paper discs, but non-resistant strains will die. A clear area will be left where the bacteria have died - an inhibition zone. 3) Make sure you use a control. This is a paper disc that has not been soaked in an
antibiotic. Instead, soak it in sterile water. You can then be sure that any difference between the growth of the bacteria around the control disc and around one of the antibiotic discs is due to the effect of the antibiotic alone. 4) Leave the plate
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for 48 hours at 25'c. 5) The more effective the antibiotic is against the bacteria, the larger the inhibition zone will be.
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How do you avoid contamination? (2)
1) The Petri dishes and culture medium must be sterilised before use, to kill any unwanted microorgansims that may be lurking on them. 2) If an inocultating loop is used to transfer the bacteria to the culture medium, it should be sterilised first by
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passing it through a hot flame. 3) After transferring the bacteria, the lid of the Petri dish shoud be lightly taped on-to stop microorganisms from the air getting in. 4) The Petri dish should be stored upside down-to stop drops of condensation
falling onto the agar surface.
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What can stem cells do?
They can divide to produce lots more undifferentiated cells. They can differentiate into different types of cell, depending on what instructions they're given.
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Where are stem cells found?
In early human embryos. They're also found in adults, in bone marrow, however these stem cells don't have the ability to turn into any cell type, only certain ones.
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How can stem cells be used?
They can be grown in a lab to produce clones and made to differentiate into specialised cells to use in medicine or research.
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What happens in therapeutic cloning?
An embryo could be made to have the same genetic information as the patient. This means that the stem cells produced from it would also contain the same genes and so wouldn't be rejected by the patient's body if used to replace faulty cells.
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Why are some people against stem cell research? (2)
They feel that human embryos shouldn't be used for experiments since each one is a potential human life. Others think that curing existing patients who are suffering is more important than the rights of embryos. The embryos used in research are
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usually unwanted ones from fertility clinics which, if they weren't used for research, would probably be destroyed but campaigners for the rights of embryos usually want this banned too. People feel that scientists should concentrate more on finding
and developing other sources of stem cells, so people could be helped without having to use embryos. In some countries stem cell research is banned. It's allowed in the UK as long as it follows strict guidelines.
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In plants, where are stem cells found?
In meristems (part of the plant where growth occurs).
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In plants, what can these stem cells be used for?
To produce clones of whole plants quickly and cheaply. They can be used to grow more plants of rare species to prevent them being wiped out.
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What is diffusion?
Diffusion is the spreading out of particles from an area of higher concentration to an area of lower concentration.
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What substances does diffusion happen in?
Solutions and gases.
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The bigger the concentration gradient...?
the faster the diffusion rate.
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What also gives a faster diffusion rate?
A higher temperature because the particles have more energy so move around faster.
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What type of molecules can diffuse through cell membranes?
Very small moelcules, like oxygen, glucose, amino acids and water.
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The larger the surface area of the membrane...?
The faster the diffusion rate, because more particles can pass through at once.
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What is osmosis?
Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.
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How can you observe the effect of sugar solutions on plant tissue? (2)
1) Cut up a potato into identical cylinders, and get some beakers with different sugar solutions in them. One should be pure water and another should be a very concentrated sugar solution, then a few inbetween. 2) Measure the mass of the cylinders,
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then leave one cylinder in each beaker for 24hours. 3) Then take them out, dry them with paper towel and measure their masses again. 4) If the cylinders have drawn in water by osmosis, they'll have increased in mass. If water has been drawn out,
they'll have decreased in mass.You can calculate the percentage change in mass, then plot a graph.
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What is the dependent variable?
The chip mass.
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What is the independent variable?
Concentration of the sugar solution.
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What are the control variables?
Volume of solution, temperature, time, type of sugar used.
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What is active transport?
The process by which dissolved molecules move across a cell membrane from a lower to a higher concentration. Particles move against the concentration gradient, therefore require an input of energy from the cell.
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What type of cell uses active transport? Why?
Root hairs as it allows the plant to absorb minerals from a very dilute solution, against a concentration gradient. This is essential for its growth.
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Where is active transport used in the human body?
In the gut when there is a lower concentration of nutrients in teh gut, but a higher concentration of nutrients in the blood.
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Give 2 examples of cells using diffusion to take in substances they need and get rid of waste products.
Oxygen and carbon dioxide are transferred between cells and the environment during gas exchange. In human, urea (a waste product produced from the breakdown of proteins) diffuses from cells into the blood plasma for removal from the body by kidneys.
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How easy it is for an organism to exchange substances with its environment depends on what?
The organism's surface area to volume ratio (SA:V).
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How can diffusion happen in single-celled organisms?
Gases+dissolved substances can diffuse directly into or out of cell across the cell membrane. It's because they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume of cell
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How does diffusion happen in multicellular organisms?
They need some sort of exchange surface for efficient diffusion.
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How are exchange surfaces adapted to maximise their effectiveness?
They have a thin membrane, so substances only have a short distance to diffuse. They have a large surface area so lots of a substance can diffuse at once. Exchange surfaces in animals have lots of blood vessels, to get stuff into and out of blood
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quickly. Gas exchange surfaces in animals are often ventilated too - air moves in and out.
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How does gas exchange happen in the lungs?
1) The job of the lungs is to transfer oxygen to the blood and to remove waste carbon dioxide from it. 2) To do this the lungs contain millions of little air sacs called alveoli where gas exchange takes place. 3) The alveoli are specialised to
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maximise the diffusion of O2 and CO2. They have: -An enormous surface area. -A moist lining for dissolving gases. -Very thin walls. -A good blood supply.
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Where are villi found?
On the inside of the small intestine - it is covered in millions and millions of them.
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What do villi do?
They increase the surface area in a big way so that digested food is absorbed much more quickly into the blood. They have a single layer of surface cells and a very good blood supply to assist quick absorption.
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How does diffusion happen in leaves?
Carbon dioxide diffuses into the air spaces within the leaf, then it diffuses into the cells where photosynthesis happens.
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What is the exchange surface of a leaf? How?
The underneath of the leaf. It's covered in little holes called stomata which the carbon dioxide diffuses in through. Oxygen and water vapour also diffuse out through the stomata.
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What controls the size of the stomata? How?
The guard cells - they close the stomata if the plant is losing water faster than it is being replaced by the roots.
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What increases the area of the exchange surface?
The flattened shape of the leaf.
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What do the walls of the cells inside the leaf form?
Another exchange surface. The air spaces inside the leaf increase the area of this surface so there's more chance for carbon dioxide to get into the cells.
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What is the diffusion summary inside a leaf?
The water evaporates from cells inside the leaf. Then it escapes by diffusion because there's a lot of it inside the leaf and less of it in the air outside.
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What is the gas exchange in fish?
The gills.
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How does gas exchange happen in fish?
Water (containing oxygen) enters the fish through its mouth and passes out through the gills. As this happens, oxygen diffuses from the water into the blood in the gills and carbon dioxide diffuses from the blood into the water.
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What is each gill made of?
Lots of thin plates called gill filaments, which give a big surface area for exchange of gases.
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What are gill filaments covered in?
Lamellae, which increase the surface area even more.
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How do lamellae increasethe surface area?
They have lots of blood capillaries to speed up diffusion. They also have a thin surface layer of cells to minimise the distance that the gases have to diffuse.
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How do lamellae maintain a large concentration gradient between water and blood?
Blood flows through the lamellae in one direction and water flows over in the opposite direction.
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miams

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Really helpful, thank you!

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