IB Biology 1: Cell Biology
Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase).
During prophase the spindle microtubules grow and extend from each pole to the equator. Also chromosomes super coil and become short and bulky and the nuclear envelope breaks down. During metaphase the chromatids move to the equator and the spindle microtubules from each pole attach to each centromere on opposite sides. During anaphase the spindle microtubules pull the sister chromatids apart splitting the centromeres. This splits the sister chromatids into chromosomes. Each identical chromosome is pulled to opposite poles. During telophase the spindle microtubules break down and the chromosomes uncoil and so are no longer individually visible. Also the nuclear membrane reforms. The cell then divides by cytokinesis to form two daughter cells with identical genetic nuclei.
What is interphase?
Interphase is an active period in the life of a cell during which many metabolic reactions occur such as protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplast.
How to find the mitotic index?
number of cells in mitosis/total number of cells
Outline the cell theory.
-All living organisms are composed of cells. -Cells are the smallest unit of life. -Cells come from pre-existing cells and cannot be created from non-living material.
State three differences between plant and animal cells.
-Animal cells only have a plasma membrane and no cell wall. Whereas plant cells have a plasma membrane and a cell wall. -Animal cells do not have chloroplasts whereas plant cells do for the process of photosynthesis. -Animal cells store glycogen as their carbohydrate resource whereas plants store starch. -Animal cells do not usually contain any vacuoles and if present they are small or temporary. On the other hand plants have a large vacuole that is always present. -Animal cells can change shape due to the lack of a cell wall and are usually rounded whereas plant cells have a fixed shape kept by the presence of the cell wall.
Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others.
-Every cell in a multicellular organisms contains all the genes of that organism. However, the genes that are activated vary from cell to cell. Genes encode for proteins and the proteins affect the cell's structure and function so that the cell can specialize. This is called differentiation. -Differentiation depends on gene expression which is regulated mostly during transcription. It is an advantage for multicellular organisms as cells can differentiate to be more efficient unlike unicellular organisms who have to carry out all of the functions within that one cell.
Outline potassium channels for facilitated diffusion in axons
-Four protein subunits with a narrow pore between them. -K ions bond to shell of water (too large to pass). -Bonds between K and water shell broken, forms bond with amino acids instead, passing through pore. -Other molecules may be too small or large, SPECIFICITY OF PUMP -Voltage-gated = imbalance of positive and negative charges -If more positive charges outside, channels close. -If more positive charges inside, K channels open and K ions diffuse through. -Closes again due to extra globular protein ball with a flexible chain of amino acids which fits inside pore to close it. 1. Channel closed 2. Channel briefly opens 3. Channel closed by ball and chain
Compare prokaryotic and eukaryotic cells
-Prokaryotic cells have naked DNA which is found in the cytoplasm in a region named the nucleoid. On the other hand, eukaryotes have chromosomes that are made up of DNA and histone protein. These chromosomes are found in the nucleus enclosed in a nuclear envelope. -Prokaryotes do not have any mitochondria whereas eukaryotes do. -Prokaryotes have small ribosomes (70S) compared to eukaryotes which have large ribosomes (80S). -In prokaryotes there are either no or very few organelles bounded by a single membrane in comparison to eukaryotes which have many of them including the Golgi apparatus and the endoplasmic reticulum.
Explain the importance of the surface area to volume ratio as a factor limiting cell size.
-When the cell increases in size so does its chemical activity. This means that more substances need to be taken in and more need to be removed. The surface area of the cell is vital for this. Surface area affects the rate at which particles can enter and exit the cell (The amount of substances that it takes up from the environment and excretes into the environment), whereas the volume affects the rate at which material are made or used within the cell, hence the chemical activity per unit of time. -As the volume of the cell increases so does the surface area however not to the same extent. When the cell gets bigger its surface area to volume ratio gets smaller. If the surface area to volume ratio gets too small then substances won't be able to enter the cell fast enough to fuel the reactions and waste products will start to accumulate within the cell as they will be produced faster than they can be excreted. In addition, cells will not be able to lose heat fast enough and so may overheat. Therefore the surface area to volume ratio is very important for a cell as diffusion pathways should be kept short.
Outline the sodium potassium pump for active transport
1. Interior of pump is open to inside of axon. 3 Na ions enter pump and attach to binding sites 2. ATP transfers a phosphate group from itself to the pump; pump changes and interior closes 3. Interior of pump opens to outside of axon and three NA ions are released outside 4. Two K ions from outside can enter and attach to their binding sites 5. Binding ofL causes release of phosphate group; causes pump to change shape so that it is only open to inside of axon 6. The interior of pump opens to inside of axon and 2 K are released inside. Sodium ions then enter and bind to pump again.
Explain the role of protein pumps and ATP in active transport across membranes.
Active transport involves the movement of substances through the membrane using energy from ATP. The advantage of active transport is that substances can be moved against the concentration gradient, meaning from a region of low concentration to a region of high concentration. This is possible because the cell membrane has protein pumps embedded it which are used in active transport to move substances across by using ATP. Each protein pump only transports certain substances so the cell can control what comes in and what goes out.
Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.
After proteins have been synthesized by ribosomes they are transported to the rough endoplasmic reticulum where they can be modified. Vesicles carrying the protein then bud off the rough endoplasmic reticulum and are transported to the Golgi apparatus to be further modified. After this the vesicles carrying the protein bud off the Golgi apparatus and carry the protein to the plasma membrane. Here the vesicles fuse with the membrane expelling their content (the modified proteins) outside the cell. The membrane then goes back to its original state. This is a process called exocytosis. Endocytosis is a similar process which involves the pulling of the plasma membrane inwards so that the pinching off of a vesicle from the plasma membrane occurs and then this vesicle can carry its content anywhere in the cell.
How do prokaryotic cells divide?
Binary fission
How do Pasteur's experiments disprove spontaneous generation on Earth?
For growth of microbes to occur, contamination was needed
List the functions of membrane proteins.
Membrane proteins can act as hormone binding sites, electron carriers, pumps for active transport, channels for passive transport and also enzymes. In addition they can be used for cell to cell communication as well as cell adhesion.
Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.
The phospholipids in the cell membrane are not solid but are in a fluid state allowing the membrane to change its shape and also vesicles to fuse with it. This means substances can enter the cell via endocytosis and exit the cell via exocytosis. The membrane then returns to its original state. In exocytosis the vesicles fuse with the membrane expelling their content outside the cell. The membrane then goes back to its original state. Endocytosis is a similar process which involves the pulling of the plasma membrane inwards so that a vesicle is pinched off it and then this vesicle can carry its content anywhere in the cell.
What are tumors a result of?
Tumors are formed when cell division goes wrong and is no longer controlled. This can happen in any organ or tissue.
Draw an E. Coli cell and outline the function of organelles
Cell wall: Protects the cell from the outside environment and maintains the shape of the cell. It also prevents the cell from bursting if internal pressure rises. Plasma membrane: Semi-permeable membrane that controls the substances moving into and out of the cell. It contains integral and peripheral proteins. Substances pass through by either active or passive transport. Cytoplasm: Contains many enzymes used to catalyze chemical reactions of metabolism and it also contains the DNA in a region called the nucleoid. Ribosomes are also found in the cytoplasm. Pili: Help bacteria adhere to each other for the exchange of genetic material. Flagella (singular flagellum): Made of a protein called flagellin. Helps bacteria move around by the use of a motor protein that spins the flagellum like a propeller. Ribosomes: They are the site of protein synthesis. Contributes to protein synthesis by translating messenger RNA. Nucleoid: Region containing naked DNA which stores the hereditary material (genetic information) that controls the cell and will be passed on to daughter cells.
Define diffusion and osmosis.
Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration. Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.
Explain passive transport across membranes by simple diffusion and facilitated diffusion.
Membranes are semi-permeable which means that they allow certain molecules through but not others. The molecules can move in and out through passive transport which is a method that does not require any input of outside energy. It can either be done by simple diffusion or facilitated diffusion. Molecules will go from a region of high concentration to a region of low concentration as they move randomly and eventually become evenly distributed within the system if they are permeable to the membrane. Simple diffusion involves the diffusion of molecules through the phospholipid bilayer while facilitated diffusion involves the use of channel proteins embedded in the membrane. The cell membrane is hydrophobic inside so hydrophobic (lipid soluble) molecules will pass through by simple diffusion whereas hydrophilic molecules and charged particles will use facilitated diffusion. Water moves through by osmosis which is also by passive transport. Osmosis involves the movement of water molecules from a region of low solute concentration, to a region of high solute concentration. So if the solute concentration is higher inside the cell than outside the cell, water will move in and vice versa.
Functions of life in chlorella
Metabolism: most metabolic pathways occur in cytoplasm Reproduction: The nucleus can divide to support cell division by mitosis Homeostasis: Contractile vacuole fills up with water and expels through the plasma membrane to manage the water content Growth: After consuming and assimilating biomass from food the algae will get larger until it divides Response: The wave action of the cilia moves the algae in response to changes in the environment (towards light) Excretion: the plasma membrane controls the entry/exit of substances including the diffusion of waste oxygen Nutrition: Photosynthesis happens inside chloroplasts to provide algae with food
Functions of life in paramecium
Metabolism: occurs in cytoplasm Reproduction: the nucleus can divide to support cell division by mitosis, reproduction is asexual Homeostasis: contractile vacuole fills up with water and expels it through the plasma membrane to manage water content Growth: assimilates biomass and gets larger until it divides Response: the wave action of cilia moves the paramecium in response to changes in the environment, towards food. Excretion: the plasma membrane control the entry and exit of substances including the expulsion of waste Nutrition: food vacuoles contain organism it has consumed
Explain how mitosis produces two genetically identical nuclei.
Mitosis is divided into four stages; prophase, metaphase, anaphase and telophase. During prophase, the chromosomes become visible under a light microscope as they super coil and therefore they get shorter and more bulky. The nuclear envelope disintegrates and the spindle microtubules grow and extend from each pole to the equator. At metaphase the chromatids move to the equator. The sister chromatids are two DNA molecules formed by DNA replication and are therefore identical. These sister chromatids are then separated in anaphase as the spindle microtubules attaches to centromere and pulls the sister chromatids to opposite poles. As the sister chromatids separate they are called chromosomes. This means that each pole has the same chromosomes (same genetic material). Finally the microtubules break down, the chromosomes uncoil and the nuclear membrane reforms. The cell then divides into two daughter cells with genetically identical nuclei.
Evaluate stem cell therapy using adult stem cells
PROS -consenting adult -low risk of tumour development CONS -difficult to obtain, deep in tissue -very limited quantities -reduced differentiation potential
Evaluate stem cell pros and cons?
PROS -may pave way for future discoveries -used to cute serious disease and disabilities -transplants are less likely to be rejected as they are genetically identical to parent -transplants do not require death of another human being -can be taken from embryo that stopped developing -taken at a stage where embryo has no nervous system and can feel no pain CONS -creation and destruction of human embryos -capable of continued divison may cause tumours/cancer -more embryos are produced than needed, excess embryos killed
Evaluate stem cell therapy using embryos
PROS: -can be obtained from excess embryos generated by IVF -large quantities -almost unlimited growth potential, totipotent CONS: -destruction of embryo (ethics) -high risk of tumour development
Evaluate stem cell therapy using cord blood stem cells
PROS: -easily obtained and stored -umbilical cords are removed at birth and discarded whether stem cells are taken or not -low risk of tumour development CONS -limited quantities -limited differentiation potential
Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.
Phospholipid molecules make up the cell membrane and are hydrophilic (attracted to water) as well as hydrophobic (not attracted to water but are attracted to other hydrophobic tails). They have a hydrophilic phosphate head and two hydrophobic hydrocarbon tails. Cell membranes are made up of a double layer of these phospholipid molecules. This is because in water the hydrophilic heads will face the water while the hydrophobic tails will be in the centre because they face away from the water. The phospholipid bilayer makes the membrane very stable but also allows flexibility. The phospholipid in the membrane are in a fluid state which allows the cell to change it's shape easily.
Question the cell theory using striated muscle, aseptate fungal hyphae, and giant algae
Striated muscle: challenges the idea that a cell has one nucleus, as it is nucleated despite being surrounded by ONE single plasma membrane. can also be very long, about 300mm. Aseptate fungal hyphae: challenges idea that cell is a single unit as it is multi-nucleated. The cytoplasm is continuous along hyphae with no membrane enclosing it, challenges idea that cells are membrane-bound. Giant algae: challenges idea that cell must be simple in structure and small in size. It is gigantic, 5-100 mm) and very complex with a single nucleus
Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis.
The first stage of cell division is interphase which is divided into 3 phases; G1, S and G2. The cell cycle starts with G1 (Gap phase 1) during which the cell grows larger. This is followed by phase S (synthesis) during which the genome is replicated. Finally, G2 (gap phase 2) is the second growth phase which separates the newly replicated genome and marks the end of interphase. The fourth stage is mitosis which is divided into prophase, metaphase, anaphase and telophase. During mitosis the spindle fibres attach to the chromosomes and pull sister chromatids apart. This stage separates the two daughter genomes. Finally, cytokinesis is the last stage during which the cytoplasm divides to create two daughter cells. In animal cells the cell is pinched in two while plant cells form a plate between the dividing cells.