Cell Biology

• What are eukaryotic cells?

  Plant and animal cells which have a cell membrane, cytoplasm and genetic material enclosed in a nucleus.

  
• What are prokaryotic cells?

  Bacterial cells which are much smaller, they have a cytoplasm and a cell membrane surrounded by a cell wall, but the genetic material is not enclosed in a nucleus, it is a single DNA loop and there may be one or more small rings of DNA called plasmids.

  
• How many micrometres (um) in a metre?

  1,000,000 (million).
• How many nanometres in a metre?

  1,000,000,000 (billion).
• What is an order of magnitude?

  Every order of magnitude is 10x greater than the one before.
• What is the cytoplasm?

  A watery solution where chemical reactions take place.
• What is the job of the cell membrane?


  To control the molecules that can enter and leave the cell.
• What is the job of mitochondria?


  Site of aerobic respiration.
• What is the job of a ribosome?


  Site of protein synthesis.
• Which structures do plant cells have that animal cells do not?

  Cell wall

  Chloroplasts

  Vacuole
• What is the job of the chloroplasts?


  Chloroplasts contain chlorophyll which are the sites of photosynthesis.
• What is the job of the cell wall?from cellulose which strengthens the cell.
• What is the job of the permanent vacuole?


  The vacuole is filled with cell sap and helps give the plant cell its shape.
• What is cell differentiation?

  As an organism develops, cells differentiate to form different types of cells. Most types of animal cells differentiate at an early stage. Many types of plant cells are able to differentiate throughout their life. In mature animals, cell division is mainly restricted to repair and replacement. As a cell differentiates it acquires different sub-cellular structures to enable it to carry out a certain function. It has become a specialised cell.
• What adaptations do sperm cells have?

  They only contain half the genetic information of a normal adult cell. They have a long tail and are streamlined making it easier to swim to the ovum. They are packed full of mitochondria providing energy for swimming. They contain enzymes allowing them to digest their way through the outer layer of the ovum.

  
• What adaptations do nerve cells have?

  They have a long axon to carry electrical impulses from one part of the body to another. The axons are covered with myelin which insulates the axon and speeds up the transmission of nerve impulses. There are synapses at the end of each cell which allow the impulses to pass from one nerve cell to another. Nerve cells have dendrites which increase the surface area so that other nerve cells can connect more easily.

  
• What adaptations do muscle cells have?

  They contain protein fibres which can change their length. They are packed full of mitochondria to provide energy for muscle contraction.
• What adaptations do root hair cells have?

  They have a root hair to increase surface area for increased rates diffusion. They don't have any chloroplasts because they are underground.

  
• What adaptations do xlyem cells have?

  They have thick walls containing lignin providing support for the plant. The end walls between the cells have broken down, allowing the cells to form a long tube so the water and minerals can flow easily. They have no internal structure making it easier for water and minerals to flow.

  
• What adaptations do phloem cells have?

  Phloem vessel cells don't have a nucleus and only limited cytoplasm. The end walls of the vessel cells sieve plates, both adaptations allowing dissolved sugars to move through the cell interior. Because phloem vessel cells have very limited cytoplasm, and so they have companion cells connected by pores containing mitochondria to provide energy to the phloem vessel cell.
• Why has electron microscopy increased biologist's understanding of sub-cellular structures?

  An electron microscope has a much higher magnification and resolution than a light microscope, and so it can be used to study cells in much more detail, which has enabled biologists to see and understand many more sub-cellular structures.
• How do bacteria multiply?

  Bacteria multiply by simple cell division (binary fission) as often as once every 20 minutes if they have enough nutrients and a suitable temperature. Bacteria can grow in a nutrient broth solution or as colonies on an agar gel plate. Uncontaminated cultures of microorganisms are required for investigating the effectiveness of disinfectants and antibiotics.
• How can we calculate the number of bacteria present after a certain amount of time?

  Number of bacteria = 2^number of rounds of division.
• How can we prepare an uncontaminated culture using aseptic technique?

  Disinfect the workspace and wear gloves and a lab coat. Flame sterilise all equipment. Heat, sterilize, and pour agar into Petri dishes. Transfer microorganisms onto agar using a sterile loop. Seal dishes and incubate at appropriate conditions (under 25').
• Why must petri dishes, culture media and inoculating loops be sterilised before use?

  To kill any unwanted microorganisms that may be on them.
• Why must the lid of the Petri dish be secured with adhesive tape?

  To prevent microorganisms from the air getting in.
• Why must the Petri dish be stored upside down?


  To prevent drops of condensation falling onto the agar surface.
• In school laboratories, why must cultures generally be incubated at 25'C?

  Because harmful pathogens are more likely to grow above this temperature.
• What are chromosomes?


  The nucleus of a cell contains chromosomes made of DNA molecules. Each chromosomes carries a large number of genes. In body cells the chromosomes are normally found in pairs.
• What is the first stage of the cell cycle?

  During the cell cycle the genetic material is doubled then divided into two identical cells. Before a cell can divide it needs to grow and increase the number of sub-cellular structures such as ribosomes and mitochondria. The DNA replicates to form two copies of each chromosome.

  
• What is the second stage of the cell cycle?

  Mitosis. In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides.

  
• What is the third stage of the cell cycle?

  Finally the cytoplasm and cell membranes divide to form two identical cells.

  
• Why is mitosis important?

  Cell division by mitosis is important in the growth and development of multicellular organisms.
• What is a stem cell?

  A stem cell is a cell that can differentiate into any other type of cell. Treatment with stem cells may be able to help conditions such as diabetes and paralysis.
• What are the functions of stem cells in embryos, in adult animals and in the meristems in plants?

  Stem cells from human embryos can be cloned and made to differentiate into most different types of human cells. Stem cells from adult bone marrow can form many types of cells including blood cells. Meristem tissue in plants can differentiate into any type of plant cell throughout the life of the plant.
• What is therapeutic cloning?

  In therapeutic cloning an embryo is produced with the same genes as the patient. Stem cells from the embryo are not rejected by the patient's body so they may e used for medical treatment.
• What are the potential risks of using stem cells?

  Transfer of viral infection, and some people have ethical or religious objections.
• How can stem cells from meristems in plants be used?

  Stem cells from meristems in plants can be used to produce clones of plants quickly and economically. Rare species can be cloned to protect from extinction. Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.
• What is diffusion?


  Substances may move into and out of cells across the cell membranes via diffusion. Diffusion is the spreading out of particles of any substance in a solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration. Some of the substances transported in and out of cells by diffusion are oxygen and carbon dioxide in gas exchange, and of the waste product urea from cells into the blood plasma for excretion in the kidney.
• What factors affect the rate of diffusion?

  The greater the concentration gradient (the difference in concentration) the faster diffusion takes place. The higher the temperature, the faster the rate of diffusion. The greater the surface area, the faster the rate of diffusion.