Studied by 22 people
State the three parts of the cell theory
Living organisms are made up of one or more cells
The cell is the smallest unit of life
Every new cell must come from a preexisting cell
Compare the use of the word theory in daily language and scientific language
Daily use - a theory is a guess, there is doubt
In scientific use: a theory has been shown to be true through repeated observations and experiments. There is no current doubt*. As of yet, no evidence has been collected that does not support the idea.
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Well substantiated= lots of evidence
Explanation of the natural world = why natural things are they way they are
Based on a body of facts = not opinion
Repeatedly confirmed = shown over and over and over again
Through observation and experiment = rigorous testing and use of the scientific method
Are not guesses = not a guess
Distinguish inductive from deductive reasoning
Definition:
Inductive reasoning involves drawing general conclusions from specific observations or evidence. It moves from specific instances to generalizations or hypotheses.
Process:
In inductive reasoning, a series of specific observations or data points are analyzed to identify patterns, trends, or regularities.
Based on these observations, a general principle or hypothesis is proposed that explains the observed patterns.
Strength:
Inductive reasoning provides probable conclusions rather than absolute certainty. The strength of an inductive argument depends on the quality and quantity of the evidence supporting the conclusion.
Inductive reasoning is more probabilistic and allows for the possibility of new evidence challenging or refining the conclusion.
Example:
All observed swans are white. Therefore, one might induce that all swans are white. However, this conclusion is tentative and subject to change if a black swan is discovered.
Definition:
Deductive reasoning involves deriving specific conclusions from general principles or premises. It moves from general statements to specific instances.
Process:
In deductive reasoning, a premise or set of premises is provided as the starting point. These premises are assumed to be true.
Logical rules (such as syllogisms) are then applied to deduce specific conclusions that necessarily follow from the premises.
Strength:
Deductive reasoning provides conclusions that are logically certain if the premises are true and the rules of logic are applied correctly.
Unlike inductive reasoning, deductive reasoning leads to conclusions that are either valid or invalid, with no middle ground.
Example:
All men are mortal. Socrates is a man. Therefore, Socrates is mortal. This conclusion follows necessarily from the premises and is considered logically valid.
Outline the process of inductive reasoning that led to the development of the cell theory
From the 17th century on, biologists examined tissues from both plants and animals (later from fungi, bacteria and protists) and saw that every specimen contained at least one or more cells.
Subcellular components have never been seen to perform the functions of life whereas full cells have.
We have observed cells coming from other cells, but never observed spontaneous generation.
Outline how deductive reasoning can be used to predict characteristics of a newly discovered organism.
The cell theory can be used to make predictions using deductive reasoning; using a general premise to form a specific conclusion.
General Premises
All organisms are made of one or more cells
Thus
Slime molds are living organisms.
Demonstrate how to make a temporary wet mount and stain a microscopic sample.
Wet Mount
In a wet mount, a drop of water is used to suspend the specimen between the slide and cover slip. This procedure is performed in the laboratory to observe motile organisms or samples that need to be stained prior to viewing with a microscope
Place a sample on the slide.
Using a pipette, place a drop of water on the specimen.
Place the edge of the cover slip over the sample at an angle and carefully lower the cover slip into place. This method will help prevent air bubbles from being trapped under the cover slip.
If there is too much water, the cover slip will slide around. Take a piece of paper towel and hold it close to one edge of the cover slip. This will draw out some water.
Staining
A drop of stain can be added when making a wet mount slide. Stains are chemicals that bind to structures within the sample and are used to make them show more clearly when being viewed.
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Iodine is one of the more commonly available stains and is used to identify starch in a variety of samples. It will stain starch as brown or blue-black. Glycogen will show as red.
Methylene Blue is useful in identifying cell nuclei and DNA.
Gram Stain divides bacteria into one of two types: Gram positive or Gram negative based on the size and composition of the cell wall.
Demonstrate how to focus the microscope on a sample
Place a slide on the stage so that it is centered under the objective lens.
Turn the revolving nosepiece so that the lowest power objective lens is "clicked" into position.
While looking at the objective lens and the stage from the side, turn the coarse focus knob so that the stage moves upward toward the objectives. Move it as far as it will go without touching the slide.
Look through the eyepiece and adjust the light source and diaphragm until you attain the maximum, comfortable level of light.
Slowly turn the coarse adjustment so that the stage moves down (away from the slide). Continue until the image comes into broad focus. Then turn the fine adjustment knob, as necessary, for perfect focus.
Move the microscope slide until the image is in the center of the field of view. Then re-adjust the light source or diaphragm in order to attain the clearest image.
Once you have attained a clear image, you should be able to change to a higher power objective lens with only minimal use of the fine focus knob. If you cannot focus on your specimen, repeat the above steps and work from objective to objective until the higher power objective lens is in place.
Demonstrate how to draw cell structures seen with a microscope using sharp, carefully joined lines and straight edge lines for labels
Define resolution and magnification.
Magnification is how much larger an object appears compared to its real size.
The shortest distance between two separate points in a microscope’s field of view that can still be distinguished as separate objects is the resolution
Compare the functionality of light and electron microscopes.
Light Microscope Electron Microscope |
Magnification | Up to ~1500x | Up to 1,000,000x |
Resolution | ~200 nm | ~0.2 nm |
Sample State | Live or dead | Only dead |
Ease of Use | Easy and accessible | Requires expertise and facilities |
Applications | Cell observation, basic processes | Ultrastructure, molecular details |
State a benefit of using fluorescent stains to visualize cell structures.
Using fluorescent stains to visualize cell structures allows for specificity and clarity in identifying particular molecules or organelles within a cell
Outline the process of visualizing specific proteins in cells using immunofluorescence technology.
Fixation: Cells are preserved using chemical fixatives (e.g., formaldehyde) to maintain their structure and immobilize proteins.
Permeabilization: Detergents (e.g., Triton X-100) are applied to make the cell membrane permeable, allowing antibodies to access intracellular structures.
Blocking: A blocking solution (e.g., serum or BSA) is used to prevent nonspecific antibody binding.
Primary Antibody Binding: A primary antibody specific to the target protein is introduced, binding directly to the protein of interest.
Secondary Antibody Binding: A fluorescently labeled secondary antibody, which recognizes the primary antibody, is applied. This step amplifies the signal and enables visualization.
Imaging: Fluorescent signals are detected and visualized using a fluorescence microscope, highlighting the spatial distribution of the target protein within the cell.
Outline the process of producing images of cell surfaces using freeze-fracture electron microscopy
Freezing: The sample (e.g., tissue or cell culture) is rapidly frozen using liquid nitrogen or another cryogen. This step preserves the cell's structural integrity by halting molecular motion.
Fracturing: The frozen sample is fractured using a microtome or a specialized device. The fracture typically occurs along the plane of least resistance, such as between the lipid bilayers of the cell membrane.
Replication: The exposed surfaces are coated with a thin layer of metal (e.g., platinum or gold) followed by carbon. This creates a replica of the fractured surface.
Removal of Organic Material: The sample is treated with chemicals (e.g., acids or detergents) to dissolve the organic material, leaving behind only the metal-carbon replica.
Examination: The replica is placed in a transmission electron microscope (TEM), where electrons pass through the sample to generate a detailed image of the fractured surface.
Analysis: The resulting images reveal the organization of membrane components, such as proteins and lipids, as well as the topology of cell surfaces.
Outline the process of visualizing specific proteins using cryogenic electron microscopy.
Sample Preparation:
The protein of interest is isolated and purified.
The sample is suspended in a thin layer of aqueous solution on a specialized grid.
The grid is rapidly frozen in liquid ethane or a similar cryogen to prevent the formation of ice crystals. This step preserves the native structure of the protein.
Data Collection:
The frozen sample is placed in a cryo-EM instrument maintained at extremely low temperatures.
A beam of electrons is directed through the sample. The low temperature minimizes radiation damage and helps preserve structural details.
Imaging:
Thousands to millions of images of the protein are captured in different orientations. These two-dimensional images contain projections of the protein’s structure.
Image Processing:
Specialized software aligns and combines the images to reconstruct a three-dimensional (3D) model of the protein.
Computational algorithms refine the resolution, enabling detailed visualization of atomic structures.
Analysis:
The 3D structure of the protein is analyzed to understand its function, interactions, and potential binding sites for drug design.
Outline the function of structures that are common to all cells.
DNA - The genetic material which carries the information of a cell to function and develop
Cytoplasm - Cytosol is the liquid part of the cytoplasm. It is a gel-like fluid substance made of water and many dissolved solutes (A1.1.5) such as salts, fatty acids, sugars, amino acids, and proteins such as enzymes (C1.1.1).
These dissolved substances are needed to carry out the metabolic processes required to keep the cell alive (C1.1.2) . If these molecules were not dissolved in water, they would not be able to perform their function, so this is where metabolic reactions happen
Plasma Membrane/Cell Membrane -Every cell has a membrane barrier separating the interior from its surroundings (B2.1.2). The membrane is a bilayer formed from phospholipids as a consequence of their hydrophobic and hydrophilic regions, creating a semi permeable region
Ribosomes - catalyzes the synthesis of polypeptides during translation
Outline the functions of cell wall
provides shape and allows the cell to withstand turgor pressure without bursting
Outline the functions of plasma membrane
responsible for regulating what materials move into and out of the cell
Outline the functions of cytoplasm
gel-like fluid substance (mostly water with many dissolved molecules), site of metabolic reactions
Outline the functions of 70s ribosome
build proteins during translation
Outline the functions of nucleoid DNA.
Nucleoid: main DNA of the cell.
DNA is not enclosed in a membrane, it is found freely in the cytoplasm
DNA is a single loop
DNA is not wrapped around proteins called histones (termed “naked”)
Define the term “naked” in relation to prokaryotic DNA.
Naked DNA is only found in prokaryotic cells and is known as such because it exists freely in the cytoplasm without being wrapped around proteins called histones
In eukaryotes, the DNA coils around proteins called histones to form structures called nucleosomes
Compare and contrast prokaryotic and eukaryotic cell structure.
1. Size:
Prokaryotic cells are generally smaller, with a diameter ranging from 0.1 to 5.0 micrometers.
2. Genetic Material:
Prokaryotic cells lack a true nucleus. Their genetic material is present in the form of a single circular chromosome located in the nucleoid region.
3. Membrane-bound Organelles:
Prokaryotic cells lack membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.
4. Ribosomes:
Ribosomes in prokaryotic cells are smaller (70S) compared to those in eukaryotic cells (80S).
5. Cell Wall:
Prokaryotic cells have a rigid cell wall composed of peptidoglycan, which provides structural support and protection.
6. Flagella:
Flagella in prokaryotic cells are simpler in structure and are used for motility.
7. Binary Fission:
Prokaryotic cells reproduce by binary fission, a form of asexual reproduction where the cell divides into two identical daughter cells.
1. Size:
Eukaryotic cells are generally larger, with a diameter ranging from 10 to 100 micrometers.
2. Genetic Material:
Eukaryotic cells have a true nucleus enclosed within a nuclear envelope. Their genetic material is organized into multiple linear chromosomes.
3. Membrane-bound Organelles:
Eukaryotic cells contain membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and chloroplasts (in plant cells).
4. Ribosomes:
Ribosomes in eukaryotic cells are larger (80S) compared to those in prokaryotic cells (70S).
5. Cell Wall:
Plant cells have a cell wall composed of cellulose, while animal cells lack a cell wall.
6. Flagella and Cilia:
Flagella and cilia in eukaryotic cells are more complex in structure and are involved in various cellular processes such as motility and sensory functions.
7. Mitosis and Meiosis:
Eukaryotic cells undergo mitosis for growth, development, and tissue repair, as well as meiosis for the formation of gametes in sexual reproduction.
Both prokaryotic and eukaryotic cells have a plasma membrane that encloses the cell and regulates the passage of materials in and out of the cell.
Both types of cells contain cytoplasm, where cellular processes occur.
Both types of cells contain ribosomes involved in protein synthesis.
Outline the functions of cilia and the flagella
Cilia and flagella are extensions from the cell surface which aid in cell movement. They are formed from modified centrioles called a basal body.
If the protrusions are short and numerous they are termed cilia. Cilia beat in coordination with each other.
If the protrusions are longer and less numerous (usually only one or two) they are termed flagella. Flagella move independently of each other.
Outline the functions of capsule and Pili
Pili*: enable the cell attach to surfaces, swap DNA with other cells and may be used to harpoon DNA in the environment
Capsule*: helps the cell keep from dehydrating and adhere to surfaces
Outline the function of 80s ribosomes
both prokaryotes and eukaryotes have ribosomes which...
catalyzes the synthesis of polypeptides during translation (D1.2.6).
are composed of two subunits that come together to form a functioning structure (D1.2.17*).
“Free” = floating in the cytoplasm synthesizing polypeptides used within the cell.
“Bound” = attached to the rough endoplasmic reticulum🟢, synthesizing polypeptides that are secreted from the cell or become integral proteins in the cell membrane
Outline the function of nucleus
Contains the DNA (A1.2.6), which stores information (A1.2.9) for making proteins via transcription (D1.2.1) and translation (D1.2.5).
Contains the nucleolus, which is where ribosome subunits (B2.2.7) are made.
Has a double membrane with pores through it (B2.2.6) which allows eukaryotic cells to separate the activities of gene transcription and translation (B2.2.2).
Outline the function of mitochondria
Mitochondria are adapted for production of ATP by aerobic cellular respiration
The mitochondrion is surrounded by a double membrane.
Mitochondria evolved by endosymbiosis
Outline the function of chloroplast
Chloroplasts are adapted for photosynthesis, which captures light energy and uses it with water and carbon dioxide to produce glucose
Within the chloroplasts are light-absorbing pigments such as chlorophyll, which give the chloroplast its characteristic green color (C1.3.9).
Chloroplasts evolved by endosymbiosis
Outline the function of endoplasmic reticulum
The RER is a series of connected flattened membranous sacs that play a central role in the synthesis and transport of polypeptides.
Has bound ribosomes (B2.2.7) which synthesize the polypeptide and release it to the inside of the RER.
The RER membrane is continuous with the nuclear envelope, which surrounds the cell nucleus.
The SER is a series of connected flattened membranous sacs that are continuous with the RER.
In contrast to the RER, smooth endoplasmic reticulum lacks ribosomes and is not involved in protein synthesis.
The main functions of SER are the synthesis of phospholipids (B1.1.9) and cholesterol (B2.1.12*) for the formation and repair of membranes.
Outline the function of Golgi apparatus
The Golgi modifies polypeptides into their functional state (D1.2.18).
The Golgi sorts, concentrates and packs proteins into vesicles (B2.2.8*).
Depending on the contents, the vesicles are dispatched to one of three destinations:
Within the cell, to organelles called lysosomes.
The plasma membrane of the cell (B2.1.4).
Secretion to the outside of the cell via exocytosis
Outline the function of vesicles
Vesicles are membrane bound sacs that contain and transport materials within cells (B2.2.9*).
Transport vesicles move molecules between locations inside the cell by budding off one organelle compartment and fusing with another.
Secretory vesicles secrete molecules from the cell via exocytosis (B2.1.13*). They are also how new phospholipids are added to the cell membrane.
Outline the function of vacuoles
Mature plant cells have a central vacuole that occupies 30% - 90% of the volume of the cell.
In addition to water storage, the main role of the vacuole is to maintain turgor pressure against the cell wall. The turgor pressure is mechanism the plants use to remain upright (D2.3.6)
Outline the function of lysosomes
Lysosomes are small spherical organelles, enclosed by a single membrane.
Contain enzymes that work in oxygen-poor areas and lower pH (C1.1.8).
The enzymes digest large molecules (C1.1.2) to degrade and recycle the components of the cell's own organelles when they are old or damaged, or if the cell is 'starving' in the absence of nutrients.
Also has an immune defense function, by digesting pathogens that have been engulfed by phagocytes (C3.2.5).
Outline the function of cytoskeleton of microtubules and microfilaments.
Cytoskeleton
Present in both prokaryotic and eukaryotic cells, the cytoskeleton is not considered to be an organelle (B2.2.1).
The cytoskeleton helps cells maintain their shape, organizes cell parts and enables cells to move and divide (D2.1.6). Several different components work together to form the cytoskeleton, including:
Microtubules
Actin filaments
Intermediate filaments
Microtubules
Microtubules are polymers of a protein called tubulin 🟢and form part of the cytoskeleton.
Microtubules are used for the intracellular transport of organelles and the separation of chromosomes during mitosis
Centrioles
Centrioles are paired cylindrical-shaped organelles composed of nine groups of three microtubules organized with radial symmetry.
Functions of centrioles include:
Arrangement of the mitotic spindle during cell division (D2.1.6).
Serve as anchor points for microtubules in the cytoplasm and for cilia and flagella (when modified to become a basal body).
List the common processes carried out by all life
Metabolism
Homeostasis
Excretion
Nutrition
Movement
Growth
Reproduction
Responses to stimuli
Define metabolism
All life has metabolism.
Metabolism is the sum of all the chemical reactions in a cell.
Viruses lack metabolism, a reason they are not considered to self-sustaining life
Define homeostasis
All life has a maintenance of homeostasis. The ability of the body to seek and maintain equilibrium and maintain conditions optimal for survival.
(D3.3.1).
Living organisms keep their internal environments within a certain range (they maintain a stable internal condition), despite changes in their external environment.
Even single celled organisms maintain homeostasis, for example by keeping concentrations of water and minerals within certain levels.
Define excretion
All organisms excrete metabolic waste matter.
Excretion is a process in which metabolic waste is eliminated from an organism.
In humans, excretion primarily occurs via lungs (B3.1.4) and kidneys (D3.3.7).
In many plants, excretion occurs via leaves, roots and stem (B3.1.7)
In unicellular organisms, excretion occurs through the cell membrane, which is one reason cells must have a large surface area to volume ratio (B2.3.6)
Define growth
All living things can grow and/or develop the lifespan.
Growth is the increase in size and mass of an organism.
Development is the transformation of the organism through its lifespan.
Define nutrition
All life obtains energy and matter.
Autotrophs use external energy sources (usually the the sun) to synthesize carbon compounds from simple inorganic substances (C4.2.6)
Heterotrophs use use carbon compounds obtained from other organisms to synthesize the carbon compounds that they require (C4.2.8)
Define movement
Adaptations for movement are a universal feature of living organisms (B3.3.1).
Sessile organisms stay in one place, whereas motile organisms are mobile.
Define reproduction
All life has the capability for reproduction
Sexual reproduction involves two parents and the fusion of haploid sex cells from each parent
Meiosis allows for a sexual life cycle with fusion of gametes (D3.1.2).
Sexual reproduction produces offspring that are genetically unique and increases genetic variation within a species
Asexual reproduction involves only one parent (D3.1.1).
Asexual reproduction produces offspring that are all genetically identical to the parent.
Binary fission and mitosis (D2.1.4) are mechanism of asexual reproduction.
Define response to stimuli.
All life can recognize and respond to changes in environmental conditions. Even single celled organisms can recognize what is going on around them, and respond to changes in the environment.
Describe characteristics of Paramecium that enable it to perform the functions of life.
The paramecium is a heterotroph, and eats smaller unicellular organisms for nutrition
The cytoplasm contains dissolved enzymes that catalyze metabolic reactions such as digestion and synthesis of cellular structures.
The paramecium can move through its environment by beating of cilia to move in different directions in response to changes in the environment.
The cell will grow until it reaches a maximum surface area to volume ratio, at which point it will divide
The nucleus of the cell divides via mitosis to make another nuclei before the cell reproduces asexually. Two paramecium can also fuse before dividing to carry out a form of sexual reproduction.
Waste products from digestion are excreted through an anal pore, an example of excretion
To maintain homeostasis, excess water within the cell is collected into a pair of “contractile vacuoles” which alternately swell and expel water through an opening in the cell membrane.
Describe characteristics of Chlamydomonas that enable it to perform the functions of life.
Chlamydomonas is an autotroph, using photosynthesis for nutrition.
The cytoplasm and chloroplast contain dissolved enzymes that catalyze metabolic reactions such as digestion, photosynthesis, cellular respiration and the synthesis of cellular structures.
A light sensitive “eyespot” allows Chlamydomonas to sense light and move to it using its two flagella, illustrating the organism's ability to respond to changes in the environment.
The cell will grow until it reaches a maximum surface area to volume ratio, at which point it will divide
The nucleus of the cell divides via mitosis to make another nuclei before the cell reproduces asexually. The nuclei can also fuse and divide to carry out a form of sexual reproduction .
The oxygen byproduct of photosynthesis diffuses out through the cell membrane, an example of excretion.
To maintain homeostasis, excess water within the cell is collected into a pair of “contractile vacuoles” which alternately swell and expel water through an opening in the cell membrane.
Compare and contrast the structures of plant, animal and fungal cells with reference to cell walls
Fungi - Present, composed of chitin and other molecules.
Animal - Absent
Plant - Present, primarily composed of cellulose
Compare and contrast the structures of plant, animal and fungal cells with reference to vacuoles
Fungi - Present as a large, permanent organelle. Used to store water and to cause turgor pressure against the cell wall
Animal - Present as small, temporary structures that expel excess water or other waste products
Plant - Present as a large, permanent organelle. Used to store water and to cause turgor pressure against the cell wall
Compare and contrast the structures of plant, animal and fungal cells with reference to chloroplasts
Fungi - Absent
Animal - Absent
Plant - Present for photosynthesis
Compare and contrast the structures of plant, animal and fungal cells with reference to centrioles
Fungi - Are absent from most fungi, except a small number that have a swimming male gamete.
Animal - Used to arrange the mitotic spindle during cell division (D2.1.6) and to serve as anchor points for cilia and flagella.
Plant - Are present in the male gametes of moss and ferns.
Compare and contrast the structures of plant, animal and fungal cells with reference to cilia and flagella
Fungi - Are absent from most fungi, except a small number that have a swimming male gamete.
Animal - Present in many animal cells, including in the male gamete
Plant - Are present in the male gametes of moss and ferns.
Describe features of skeletal muscle fibers that make them an atypical cell.
Skeletal muscle fiber cells result from the fusion of multiple cells. This results in a single large cell that has multiple nuclei
Also visible are the striations due to the differences in size between the thick (myosin) and thin (actin) filaments of the myofibril.
Describe features of aseptate fungal hyphae that make them an atypical cell.
Hyphae are the tubular projections of multicellular fungi that form an underground filamentous network (mycelium). Fungal hyphae are sometimes not divided up into individual cells (called aseptate hyphae), resulting in a continuous cytoplasm along the length of the hyphae.
Aseptate hyphae are not made of clearly defined individual cells, rather continuous structures with multiple nuclei.
Except for yeast, most fungi grow as collections of filaments called hyphae. A mass of hyphae make up the body of the fungus.
Describe features of red blood cells that make them an atypical cell.
Red blood cells, also called erythrocytes, are the most common blood cells and function in oxygen transport in vertebrates.
During their maturation, red blood cells discard their nucleus and mitochondria. This makes the cells very small (B2.3.5), increasing their surface area to volume ratio (B2.3.7) for efficient gas exchange (B3.1.2) and the ability to move through narrow capillary vessels (B3.2.1).
a eukaryotic cell without a nucleus or mitochondria!
Describe features of phloem sieve tube elements that make them an atypical cell.
Sieve tube elements are specialized cells that are part of the phloem, the tissue that transports organic compounds made during photosynthesis throughout a plant (B3.2.18).
Sieve tube elements lose their nucleus and other organelles during their development. This allows the cells to have more space for transport of phloem sap.
a eukaryotic cell without organelles!
Sieve tube elements are connected to companion cells which have a nucleus and mitochondria and provide the sieve tube elements with the materials to stay alive.
Compare the number of nuclei in aseptate fungal hyphae
Multiple
Compare the number of nuclei in skeletal muscle
Multiple
Compare the number of nuclei in red blood cells
None
Compare the number of nuclei in phloem sieve tube elements
None
Explain the origin of mitochondria and chloroplast with reference to the endosymbiosis.
What is Endosymbiosis?
Scientists hypothesize that chloroplasts and mitochondria evolved from small symbiotic prokaryotes that lived within other, larger host cells.
Symbiosis is an interaction between two different organisms living in close physical association, typically to the advantage of both.
In endosymbiosis, one cell lived within the other and became increasingly interdependent until the unit could only exist as a whole.
Endosymbiosis in relation to chloroplasts and mitochondria
First, the symbiotic ancestors of mitochondria may have been aerobic bacteria that were able to use oxygen in aerobic cellular respiration (B2.2.4). An ancestral host cell may have ingested some of these aerobic cells. Instead of being digested, some of these bacterial cells might have remained alive and continued to perform respiration within the host cell.
Since almost all eukaryotes have mitochondria but only some have chloroplasts, it is likely that mitochondria evolved first.
The ancestors of chloroplasts could have been photosynthetic bacteria that lived inside a larger host cell. Instead of being digested, some of these bacterial cells might have remained alive and continued to perform photosynthesis (B2.2.5) within the host cell.
Describe the genetic, structural and behavioral evidence for the endosymbiotic theory.
STRUCTURAL EVIDENCE
Similar to prokaryotic cells, both mitochondria and chloroplasts are the same approximate size and shape as prokaryotes.
Additionally, mitochondria and chloroplasts have a double membrane (both an inner membrane and an outer membrane). This suggest they have their own cell membranes (inner membrane) plus the cell membrane that resulted from the engulfing by the primitive cell (outer membrane).
Both mitochondria and chloroplasts also have 70s ribosomes (A2.2.5) whereas eukaryotes have 80s ribosomes.
GENETIC EVIDENCE
Both mitochondria and chloroplasts:
have circular naked DNA like that of prokaryotic cells (A2.2.5) whereas eukaryotes have linear DNA wrapped around histone proteins A1.2.13)
share common DNA sequences with prokaryotes (A3.2.6)
FUNCTIONAL EVIDENCE
Both mitochondria and chloroplasts:
move independently within the eukaryotic cell
reproduce independently
of the host cell through a process similar to binary fission
are inhibited by antibiotics as are prokaryotes (C3.2.13)
Outline the benefits of cell specialization in a multicellular organism.
Every cell in a multicellular organism is specialized for a function, so:
They can focus on fewer tasks at once and do the work more efficiently while saving energy by not performing other tasks
They can have a specialized structures and metabolism
As they do one (or few) things all the time, they evolve faster in that particular tasks
Define differentiation.
The process by which cells become specialised to carry out specific functions.
Describe the relationship between cell differentiation and gene expression.
Technically, Organisms in the same species share most of their genome, so that means all cells in a multicellular organism have the same genes, but out of the estimated 20,000 genes in the human genome, about 4,000 are expressed in nearly all cell types.
These “housekeeping” genes code for proteins that are associated with basic cellular functions
So If all cells in an organism contain the same DNA, how do they specialize in shape and function?
Gene Expression can be defined as the process by which the information encoded in a gene is turned into a function. Often in gene expression, a sequence of DNA (the gene) is transcribed to form RNA (D1.2.1) which is then translated to form a protein
Differentiation occurs when different cell types express different genes (D2.2.1).
Genes that are not “housekeeping genes” are differentially expressed in different cell types. This means that some cell types express the gene whereas other cell types don’t.
regulated by proteins that bind to specific base sequences in DNA
So, the different functions of cells arise from differently expressing these genes
Stem cells are able to specialize to become different cell types by differentially turning off some genes and activating others
The expression of genes in an organism can be influenced by the environment, including the external world in which the organism is located or develops, as well as the organism's internal world, which includes such factors as its hormones and metabolism.
Drugs, chemicals, temperature, and light are among the external environmental factors that can determine which genes are turned on and off, thereby influencing the way an organism develops and functions.
In mammals hormones can be proteins or steroids.
The protein hormones do not enter the cell, but bind to receptors in the cell membrane and mediate gene expression through intermediate molecules (C2.1.7*).
Steroid hormones enter the cell and interact with steroid receptor proteins to control gene expression
List groups of organisms that are multicellular.
Most Algae
Most Fungi
Plants
Animals
Outline the steps in the evolution of multicellularity.
the first possible evidence of multicellular life dating to about 2.5 billion years ago.
What is multicellularity?
Multicellular organisms are composed of more than one cell. In a multicellular organism, the cells specialize and lose the ability to live independently.
Evolution
Multicellularity has evolved independently many times in eukaryotes.
Formation of cellular clusters from single cells.
Differentiation of the cells within the cluster for specialized functions.
Two Hypothesis
A group of independent cells come together
When a unicellular organism divides, the daughter cells fail to separate, resulting in an aggregate of identical cells
Many primitive multicellular organisms probably experienced both unicellular and multicellular states, providing opportunities to forego a multicellular lifestyle.
Cells that live in clusters may have a selective advantage over cells that live independently.
Predation is a selective pressure that is hypothesised to lead to multicellularity. Multiple experiments have demonstrated that being a part of a cluster of cells provides a survival benefit
Once clusters of cells are are established, cells can begin to serve specialized functions. This occurs through the differentiation of cells
Note 
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