Topic 1 - Cell Theory

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2.1.1 What is the cell theory

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All living organisms are made of cells.
Multicellular organisms (humans) are composed of many cells while unicellular organisms (bacteria are composed of only one cell.
-Cells are the basic unit of structure and smallest unit of life. ( they can exist on their own)
-Cells come from pre-existing cells and cannot be created from non-living material.

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What is a virus

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A non-cellular structure consisting of DNA or RNA surrounded by a protein coat

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Define organelle

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A discrete structure within a cell that has a specific function, it also needs to be covered by its own membrane.

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2.1.4 Compare the sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells using appropriate SI units.

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Molecules = 1nm
Cell Membrane =10 nm
Viruses= 100nm
Bacteria= 1um
Organelles = 10um
and Most cells = 100um

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2.1.6 What is the importance of the surface area to volume ratio as a factor limiting cell size.

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When a cell grows, the volume increases at a faster rate than the surface. Thus as the cell grows the surface to volume ratio decreases. A cell needs the surface area in order to carry out metabolic functions(chemical reactions), and as a cell grows it needs to carry out more and more reactions.Therefore it must maintain a certain surface area to volume ratio and has a limited size.

The surface area of the cell is vital as it affects the rate at which particles can enter/exit the cell (materials that are amde/used within the cell hence chemcal activity per unit of time)

eg: cells will not be able to lose heat fast enough and overheat

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2.1.7 What properties to multicellular organisms show?

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They show emergent properties.
Cells form tissue, tissues form organs, organs form organ systems and organ systems form multicellular organisms.

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2.1.8 Why do multicellular cells differenciate?

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Differentiation depends on gene expression which is regulated mostly during transciption. It is an advantage because cells can differenciate to be more efficient unlike unicellular organisms who have to carry out all the functions of life. Genes encode for proteins and affect the cells' structure and function so that they can specialize.
All cells contain genes but do not use all of them. The cells of a multicellular organism differenciate to carry out specialised functions by only expressing some of their genes.

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2.3.4 What are the differences between prokaryotic and eukaryotice cells?

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Both have cell membrane and carry out functionso of cells. ( metabolic functions and reproduction etc)

PC have naked DNA named nucleiod, EC have chromosomes made up of DNA and protein. Prokaryotic cells have
no organelles (nucleus, mitochondria etc) unlike the EC
-PC has one cirucular loop of Dna that is located in the cytoplasm where as in EC it is arranged in a complex manner with many proteins inside a nuclear envelops.
-PC is smaller thn EC
-PC has 70s ribosomes and EC has 80s ribosomes

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2.3.5 What are three differences between plant and animal cells.

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Plant cells have cell walls while animal cells dont.
Plant cells have chloroplasts while animal cells don't.
Animal cells contain mitochondria and plant cells do not.

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2.3.6 What are cell wall and extracellular cellular components for?

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Plant cell wall contains cellulose microfribrils which helps to maintin the cell's shape and prevents bursting from high pressure. It laso prevents excessive water uptake by osmosis and it is why plants can hold themselves up against gravity
Animal cells contain glycoproteins in matrix which are involved in the support, movement and adhesion of cell.

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2.4.2 How do hydrophobic and hydrophilic properties of phospolipids help to mantain the structure of the cell membrane?

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They have a hydrophilic phosphate head and two hydrophobic hydrocarbon tails. The head of the phospholipid is polar and hydrophilic, and these heads make up the outside of the phospholipid bilayer.
The tail of the phospholipid that is located inside the membrane is nonpolar and hydrophobic.
Because one end is facing outwards(facing the water) and one end facing inwards(facing the centre), the phospholipids naturally form bilayers enabling the phospholipids to form a stable structure. The phospholid is fluid which allows the cell to change shape easily

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2.4.3 What are the functions of membrane proteins?

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Membrane proteins perform many tasks which help the cell with its functions. They act as hormone binding sites, enzymes, electron carriers, channels fr passive transport and pumps for active transport.

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2.4.4 What is diffusion and osmosis?

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Diffusion- it is the total movement of particles from a region of higher concentration of that particle to a region of lower concentraion of the same particle

[the difference in concentration that drives diffusion is called a concentration gradient.

Osmosis- it is the passive movement of water molecules, across a partially permeable membrane from a region of lower solute concentration to a region of hige solute concentration.

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2.4.5 What happens in passive transport across membranes during simple diffusion.

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Transport in membranes happens naturally ( no energy required) if there is a concentration gradient between one side of the membrane and the other. The concentration gradient drives diffusion across the membrane.

Simple diffusion involves the diffursion of molecules through the phospholipid bilayer while facilatated diffusion involves he use of channel proteins embedded in the membrane. The cell membrane is hydrophobic inside so hydrophobic (lipid solubles) molecules will pass through by simple diffussion whereas hydrophobic molecules and charged molecules will use facilitated diffusion.

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2.4.6 What is the role of protein pumps and ATP in active transport across membranes.

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During active transport, the movement of subtances move through the membrance using energy from ATP. The advantage of active transport is that the substance being transported goes against the gradient ( it goes from where there is a lesser concentration to a greater concentraion)
This is possible because protein pumps in the cell membrane function in transporting particles across a membrane against concentration membranes with energy frm ATP.

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2.4.7 How are vesicicles used to transport materials within the rough endoplasmic reticulum, golgi apparatus and plasma membrane?

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Vesicles are membranous sacs in which materials are stored and transported throughout the cell. In order for the materials within a vesicle to go through a membrane (organelles/ plasma membrane), the membranous vesicle becomes part of the organelle's membrane/plasma, releasing the materials inside. The materials that were inside the vesicle are now free on the opposite side of the membrane.

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2.4.8 Describe the membrane's fluidity during endocytosis and exocytosis.

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Endocytosis is the movement of material into a cell by a process in which the plasma membrane engulfs extracellular material, forming membrane-bound sacs that enter the cytoplasm.
Exocytosis is the movement of material out of a cell by a process in which intracellular material is enclosed within a vesicle that moves to the plasma membrane and fuses with it, releasing the mateial outside the cell.

The cell membrane is fluid in that is constantly in motion. The movement of the phospholipds changes the membrane's shape, and allows for temporary holes in the membrane that let materials flow in and out of the cell. If the membrane were not fluid in nature, it would not be able to fuse with vesicles in endocytosis and exocytosis.

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What does the cell-division cycle involve?

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Interphase, mitosis and cytokinesis

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2.5.3 What happens during interphase?

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Interphase is an active period in the life of a cell when many biochemical reactions occur, as well as DNA transcription and DNA replication.

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2.5.4 What happens during the four phases of mitosis. ( prophase, metaphase, anaphase and telophase)

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During mitosis, chromatin fibers become tightly coiled and can be seen as chromosomes. The chromosomes appear as two identical sister chromatids joined at the centromere. The mitotic spindle begins to form in the cytroplasm.Some of the microtubles that make up the spindle attach to the chromosomes.
In metaphase, the chromosomes line up on the cell equator, with each sister chromatid facing a different pole of the cell.
During anaphase, the centromere replicates and the sister chromatids separate. These new chromosomes move to opposite poles, so that each pole of the cell contains a complete set of chromosomes.
During telophase, the microtubles elongate the cell, further separating the two poles. Then the parent cell's nuclear envelope is broken down and fragments are used to form new nuclear envelopes.

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2.5.5 How does mitosis produce genetically identical nuclei?

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During mitosis, pairs of two identical chromosomes are pulled to opposite ends of the cell. These identical chromosomes contain the same genetic information as the chromosomes of the parent cell, so they are genetically identical. The two identical sets of chromosomes become the nuclei of the two daughter cells.

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What is the differences between mitosis and cytokinesis between animal and plant cells?

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A difference exist because plants have a cell wall. Mitosis in plant involves the formation of a cell plate that seperates the two daughter cells, while in animal cells use a clevage furrow to seperate the two new cells. Plant cells also lack the centriole involved in animal cell mitosis.

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2.5.6 What do mitosis engage in?

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Growth, embryonic development tissue repair and asexual reproduction

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2.5.2 What are the results of uncontrolled cell division which can occur in any organ?

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Tumours (cancer)

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2.1.2 What are the evidence for the cell theory?

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-Discovery of the microscope.
-Sealed and open container experiment

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2.1.3 What carry out all the functions of life?

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Unicellular organisms carry out the funtions of life including metabolism, response, homeostasis, grwoth, reproduction and nutrition.

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2.1.9 What is the stem cell capable of doing ?

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Skin needs to be replaced frequently, stem cells have the ability to produce a wide range of cells which means they are pluripotent.

They retain their ability to divide and produce many different cells by cell division and differenciation.

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2.1.10 What is the therapeutic use of stem cells?

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Bone marrow transplants. Stem cells found in bone marrow give rise to red blood cells, white blood cells and platelets in the body. This stem cells can be used in bone marrow transplant to treat people who have leukemia.

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2.2.2 a ) Cell Wall

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Protects the cell from outside environment and mantains the shape.

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2.2.2 b) Plasma membrane

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Semi-permeable membrane that controls the substances moving into and out of the cell.

Substance and pass through either by active or passive transport

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2.2.2 c) Cytoplasm

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contains many enzymes used to catalyze chemical reactions of metabolism and contains the nucleiod and ribosomes.

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2.2.2 d) Pili and flagella

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P- Helps bacteria adhere to each other for the exchange of genetic material
F- Helps bacteria move around

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2.2.2 e) Ribosomes

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Protein synthesis site that contributes by translating messenger RNA

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2.2.2 f) Nucleiod

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Contains naked DNA which stores the hereditary material (genetic information) that will be passed on to daughter cells.

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2.2.4 What do prokaryotic cells divide by

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Binary Fission.
It is a method of asexual reproduction involving the splitting of the parent organism into two seperates.

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2.3.2 a) Ribosomes

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Protein synthesis site that contributes by translating messenger RNA
Can be found in cytoplasm or attached to the rough endoplasmic reticulum.

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2.3.2 b) Rough Endoplasmic Reticulum

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Modify proteins to alter their function or destination. Also synthesizes proteins to be excreted from cell.(Proteins can be used or sent out)

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2.3.2 c) Lysosome

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uses hydrolytic enzymes to digest macromolecules such as proteins and lipids into their monomers

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2.3.2 d) Golgi Apparatus

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recieves many of the products of the REr and further modifies them to be packaged into final destination.

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2.3.2 e) Mitochondrion

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site of aerobic cellular respiration. Converts chemical energy into ATP using oxygen

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2.3.2 f) Nucleus

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Contain chromosomes and hereditary mateial
contains the dna which controls genotype for the cell