Biology Topic 1 Flashcards PDF

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Biology Notes from lecture (Taken directly from from the syllabus)...

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1.1 Introduction to Cells List the key statements of the cell theory.

Outline three exceptions to the cell theory.

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Living organisms are made up of one or more cells. There is no smaller unit of life than cells. Every new cell must come from a pre-existing cell.

Giant algae (example, Acetabularia species): Can be up to 10 cm in length, Single nucleus. Striated muscle cell: Very long (up to 30 cm in length), Multiple nuclei. Aseptate fungi: Filamentous hyphae without cross walls (septa), Multiple nuclei. These exceptions oppose the idea that cells have a single nucleus and that they are small (a typical eukaryotic cell’s size ranges from 10 μm to 100 μm). However, these few discrepancies are not enough to invalidate the cell theory.

State and define the seven functions of life displayed by all living organisms.

1. 2. 3. 4. 5. 6. 7.

Outline the functions of life, using the unicellular organisms Chlamydomonas and Paramecium as examples.

Metabolism: Sum of all chemical reactions within the cell or organism. Reproduction: Production of offspring. Homeostasis: Maintaining the internal environment. Nutrition: Consuming materials for growth and repair. Nutrients are a source of energy or matter to build the organism. Excretion: Removal of the waste products of metabolism. Response: Sensing and responding to a stimulus. Growth: Increase in cell number or size

State the equations to calculate: The magnification of images. The actual size of an object when a scale bar is present.

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Line X-Y has an actual size of 170 μm. Calculate the drawing magnification.

These measurements must be in the same units. The answer is in the same units as given by the scale bar.

Line X-Y has an actual size of 170 μm. Step 1: Measure the size of line X-Y using a ruler Step 2: Convert this number to μm Step 3: Divide the measured size in μm by the actual size Drawings of cells should be done with a sharp pencil. Single, clear outlines of visible features should be drawn. Avoid sketchy lines and shading. Draw features to scale. Labelling lines should be drawn using a ruler and should not cross each other. Make sure each labelling line touches the object it is labelling.

Magnification of the drawing, with scale bar.

The scale bar represents a size of 5μm Step 1: Measure the size of the scale bar using a ruler Step 2: Convert this number to μm Step 3: Divide the measured size of the scale bar in μm by the actual size the scale bar represents In this example, only the scale bar is needed to calculate the magnification of the image.

Calculate the actual diameter of the cell.

Explain how surface area to volume ratio limits the size of cells.

The scale bar represents a size of 5μm Step 1: Measure the diameter of the drawing of the cell Step 2: Measure the size of the scale bar using a ruler Step 3: Divide the diameter by the measured size of the scale bar Step 4: Multiply the answer by the size the scale bar actually represents

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Multicellular organisms (organisms consisting of more than one cell) show 1 properties.

In multicellular organisms, cells have

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The rate at which metabolic reactions occur (use of raw materials and production of waste materials and heat), depends on the volume of the cell. The larger the volume, the greater the metabolic rate. The rate at which raw materials enter the cell and waste materials and heat leave the cell, depends on the surface area of the cell. The larger the surface area, the greater the rate of exchange of materials. As cell size increases, volume increases faster than surface area. As cell size increases, the surface area to volume ratio decreases. If a cell is too large, it cannot take in raw materials nor export waste materials fast enough to function and it may overheat. Multicellular organisms (organisms consisting of more than one cell) show (1) emergent properties. Emergent properties can be summarized as: The whole is greater than the sum of the individual parts. For example: The heart is an organ and its function is to pump blood. Cardiac muscle cells alone do not have this function. They must work together with valves, the pacemaker, and neurons connecting the heart to the brain. The pumping function is an emergent property of all these component parts of the heart interacting together. Cell division (mitosis) ensures all cells in a multicellular organism are genetically identical. So every cell in the body has a full set of genes (or genome). During the differentiation of a cell, only some of the genes are expressed. Other genes are not

specialized functions. How does cell differentiation occur?

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expressed. In each type of specialized cell, a unique subset of genes will be expressed. Gene expression results in proteins being made that determine the function of the cell.

For example: Insulin is only produced in pancreatic beta cells.

What are the two key characteristics of stem cells?

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Stem cells can continually divide (self-sustaining).

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Stem cells are undifferentiated (unspecialized). ○ They can differentiate in different ways to produce different cell types.

How does the ability of stem cells to divide and differentiate in different ways make them necessary for embryo development?

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After fertilization, a zygote is formed in all multicellular organisms. After the formation of the zygote, there is a large increase in the number of cells (by mitosis). This relies on the ability of stem cells to continually divide. Early embryonic stem cells are capable of becoming any type of specialized cell (pluripotent stem cells). Subsequently, cells of the embryo start to commit to different pathways of cell differentiation and become limited in the types of specialized cells they can form (multipotent stem cells). Embryonic development results in a unique body pattern with organs and tissues comprising specialized cells. Fully specialized cells (such as muscle cells or neurons), are no longer flexible to form other types of specialized cells. Some stem cells (of limited flexibility) remain in fully developed organisms. In humans, these include blood cell stem cells and skin stem cells.

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How does the ability of stem cells to divide and differentiate in different ways make them attractive for therapeutic uses?

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What is Stargardt’s disease? Describe the use of stem cells in the treatment of Stargardt’s disease.

Describe the use of stem cells in the treatment of leukemia

Therapeutic uses of stem cells include replacing cells that have been damaged or lost by disease or accidents. These are known as cell-based therapies. Large numbers of cells can be grown. For example, skin stem cells can be grown to produce skin grafts for burn victims. Embryonic stem cells can differentiate into any type of specialized cell. They offer potential benefits to patients suffering from diseases for which there are no therapeutic cures. For example, pancreatic islet beta cells can be developed to treat type I diabetes. However, the use of embryos has ethical implications. Cord blood stem cells and adult stem cells offer an alternative but they are limited in the types of specialized cells they can differentiate into.

Stargardt’s disease is a genetic disease that causes macular degeneration in children and young adults. ● ●

Photoreceptor cells in the retina become damaged and are progressively lost. Patients gradually lose their vision, usually resulting in them being classified as legally blind.

Patients with Stargardt’s disease have been treated using embryonic stem cells. ● ● ● ●

What is leukemia?

Large numbers of cells (tissues) can be made.

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Scientists obtained stem cells from days-old human embryos and made them develop into retina cells. Many thousands of retina cells were then injected into the patients’ eyes. The patients have showed improved vision and no harmful effects of the treatment. Clinical trials are ongoing to optimize and ensure the long-term safety of this treatment. Leukemia is a type of cancer that causes a high number of abnormal white blood cells to be produced by bone marrow. Adult stem cells can be used to restore healthy bone marrow in leukemia patients. Fluid is taken from the bone marrow of the patient’s pelvis. Healthy blood stem cells are identified and frozen. Blood stem cells can also come from a healthy, matching donor. The patient receives a high dose of chemotherapy to kill the cancer cells in the bone marrow. The patient's bone marrow can no longer produce blood cells. The stored or donated blood stem cells are injected into the patient and enter the bone marrow via the bloodstream. The bone marrow regains its ability to produce healthy blood cells.

What are the ethical implications of using: Adult stem cells Cord blood stem cells Stem cells from embryos created in vitro ...for therapeutic uses?

1.2 Ultrastructure of cells Light microscopes and electron microscopes differ in their resolution. ● Define the term resolution. ● Distinguish the resolution of light and electron microscopes.

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Resolution is the smallest distance apart two objects can be in order for them to appear distinct. The resolution of a light microscope is approximately 200 nm. Resolution in light microscopes is limited by the wavelength of visible light. 200 nm is half the wavelength of visible light.The resolution of an electron microscope is better than 1 nm. Beams of electrons have a wavelength of less than 1 nm, so electron microscopes have a much higher resolution than light microscopes (at least 200 times higher). Magnification only increases the size the object appears. High magnification and low resolution will give a blurry image. High resolution allows for sharp images at high magnification. The invention of the electron microscope has led to great advancements in the understanding of cell structure.

Fill in the blank: Answers Unicellular, simple, Compartments, bacteria, archaeans.

According to their structure, cells are either classified as prokaryotic or eukaryotic. Prokaryotes are (1) organisms. Electron micrographs have revealed the structure of prokaryotic cells is (2) with no internal (3) surrounded by membranes. Two of the three major categories (or domains) of life are prokaryotes, these are the (4) and (5) .

Draw and label a diagram of a prokaryotic cell based on the electron micrographs of the bacterium Escherichia coli. If there are too many structures of one kind in each cell, draw their appearance to annotate the diagram, indicate they are found throughout

Outline the division of a prokaryotic cell by binary fission.

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The chromosome is replicated and each identical copy is moved to either end of the cell. The cell elongates. New cell wall forms and plasma membrane pinches in. Cross walls form two separate cells. The two new cells separate. Interesting fact: In optimal conditions the bacterium E. coli can divide in as little as 20 minutes. This means one cell can form over a million cells in a little over 9 hours!

Fill in the Blanks

What are the advantages of compartmentalization in eukaryotic cells?

(1) Eukaryotes include organisms in the kingdoms protoctists, fungi, plants, and animals. Electron micrographs have revealed eukaryotic cells have cells with a more (2) complex structure. They have compartments surrounded by (3) membrane. These compartments are termed (4) organelles. ●

Different metabolic processes can be separated. For example, the reactions specific to aerobic respiration in mitochondria. ○ ○

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High concentrations of enzymes specific for each process can be achieved. Different metabolic processes may require different environments, such as pH. Therefore, conditions can be optimized for each metabolic process, while allowing both processes to occur in the same cell.

Hydrolytic enzymes that can damage the cell can be separated. For example, in lysosomes. Allows for a greater surface area for those processes that occur within the cell membrane. For example, the production of ATP by chemiosmosis.

Draw and label a diagram of a whole eukaryotic cell based on the electron micrograph of the B lymphocyte.

Draw a representative image of the cell, including each cell structure that you can identify. Make sure you draw each membrane-bound organelle with the correct number of membranes and to scale. Be aware that some eukaryotes also have a cell wall. The ultrastructure of an exocrine gland cell (from the pancreas) is shown in the electron micrograph below. Label the organelles present and based on their presence and abundance, deduce the function of the cell

Exocrine gland cell (pancreas): In the cell, there are large amounts of RER and many vesicles. The very dark color of the vesicles indicates they contain proteins for secretion. The function of exocrine cells of the pancreas is to synthesize and secrete digestive enzymes

. The ultrastructure of a palisade mesophyll cell is shown in the electron micrograph below. Label the organelles present and based on their presence and abundance, deduce the function of the cell.

Palisade mesophyll cell: In the cell, there are several chloroplasts. Palisade cells are the main sites of photosynthesis in the leaf.

1.3 Membrane structure An amphipathic molecule has both hydrophilic and hydrophobic regions

Phospholipids are amphipathic.

The phosphate head is both polar and charged so it will attract polar water molecules (hydrophilic). The fatty acid tails are non-polar and will not attract polar water molecules (hydrophobic).

Define amphipathic. Label the diagram representing a phospholipid and annotate it to describe the property of each part. Explain how phospholipids form a bilayer in an aqueous environment.

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Phospholipids are amphipathic. The phosphate head is hydrophilic and the fatty acid tails are hydrophobic. Due to this, a bilayer self-assembles in water. The phosphate heads are attracted to water. Therefore, the phosphate heads are on the outside of the bilayer. The fatty acid tails are not attracted to water and are attracted to each other. Hence, the fatty acid tails are on the inside, positioned away from the water. The surface of the bilayer is hydrophilic and the inside of the bilayer is hydrophobic.

The arrangement and properties of the phospholipids in a bilayer determine the nature of substances that can pass freely through a plasma membrane.

List the evidence that led Danielli and Davson to propose their model of the plasma membrane.

Phospholipids ● Phospholipids were extracted from a red blood cell. ● The surface area of the extracted phospholipids was twice the surface area of the red blood cell. ● Concluding phospholipids were present in a bilayer. Proteins ● Membranes from red blood cells contain proteins. ● Danielli and Davson proposed a protein coat on each side of the phospholipid bilayer to explain the differential permeability of the plasma membrane. ● This implied the phospholipids were held in fixed positions by the protein layers. Electron micrographs ● The plasma membrane appeared as two dark bands on the outside with a light band in between. ● In electron micrographs, proteins appear very dark and phospholipids appear light. ● This supported the Danielli and Davson model.

Outline evidence for the falsification of the Davson-Danielli model

Freeze fracture electron micrographs ● Fracturing frozen cells allowed the outer phospholipid layer to be removed. ● Micrographs showed globular proteins present on the upper surface of the inner phospholipid layer. Protein extraction ● Proteins extracted from the plasma membrane were globular and varied in size. ● Parts of their surface were hydrophobic. ● Suggesting proteins were embedded within the phospholipid bilayer and their hydrophobic regions could attract the fatty acid tails. These findings refuted the idea of proteins forming layers on the surface of the plasma membrane.

The absence of a protein coating suggested the phospholipids were not fixed in position. X ray diffraction ● At higher temperatures, the membrane behaved as a liquid. Fluorescent labels ● Membrane proteins of two cells were linked to two different colored fluorescent labels. ● The two cells were fused. ● Initially the newly formed cell had two distinct regions of color. ● After a short time, the two different colors were fully mixed. These findings demonstrated that phospholipids and proteins were free to move within the membrane. Nature of science: New technologies and techniques led to new evidence allowing one model to be falsified and a new model being proposed. The name fluid mosaic model was proposed because:

Draw and label a diagram of the fluid mosaic model of the plasma membrane, as proposed by Singer and Nicolson.

-The phospholipids and proteins can move so the membrane is fluid and flexible. Globular proteins are arranged randomly in the phospholipid bilayer – like a mosaic.

List the roles of proteins in the plasma membrane.

Plasma membrane proteins have diverse roles: Transport proteins ● ●

Channels to allow substances to passively move through the membrane. Pumps for active transport of substances across the membrane.

Enzymes ●

Immobilized in the membrane. For example, in epithelial cells of the small intestine.

Glycoproteins ●

Cell to cell communication

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Cell to cell recognition ○ Antigens, for example ABO blood group.

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Cell adhesion

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Receptors for chemical signals, such as hormones.

Binding cells together. For example, tight junctions.

The diagram below shows the structure of the steroid, cholesterol. Label the hydrophilic and hydrophobic regions of the molecule. How would a cholesterol molecule be positioned between phospholipid molecules in the plasma membrane of animal cells? What is the role of

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Cholesterol is a prominent component of mammalian membranes. Cholesterol reduces the movement of phospholipids.

cholesterol in the plasma membranes of mammalian cells?

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Reducing membrane fluidity. Increasing membrane stability. If the membrane is too fluid, the permeability of the membrane to substances, such as ions, increases. + + 2+ Maintaining or generating differences in concentrations of ions (such as, H , Na ,or Ca ) across membranes, is essential for life. Hence, it is important that the correct level of membrane fluidity is achieved.

1.4 Membrane Transport Which of the following substances will move freely through the phospholipid bilayer: H2O,CO2, Amino acids, Glucose, O2, Fatty acids, Urea, Hydrogen ions (H+), Chloride ions (Cl−)

The phospholipid bilayer is not permeable to all substances, it is partially permeable. Use your knowledge of the properties of the phospholipid bilayer to explain its partial permeability to different substances.

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To move through the phospholipid bilayer, substances pass via gaps between the phospholipids. The two major factors that impact on permeability, are size and charge. The inside of the phospholipid bilayer is hydrophobic/non-polar due to the fatty acid tails. Small non-polar mol...