Cell Structure (DP IB Biology)

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  • What is a cell?

    Cells are the basic structural units of living organisms.

  • What does cell theory state?

    Cell theory states that:

    • All living organisms are made up of one or more cells

    • Cells are the smallest units of life and are the basic functional unit in living organisms

    • New cells are produced from pre-existing cells

  • True or False?

    The flow diagram below shows deductive reasoning. (NOS)

    observation → conclusion → theory

    False.

    The flow diagram observation → conclusion → theory shows inductive reasoning and not deductive reasoning.

    Deductive reasoning moves from the general to the specific, so a deductive flow diagram might be:

    theory → hypothesis → observation

  • How is deductive reasoning used in science? (NOS)

    Deductive reasoning in science involves using widely accepted theories to develop specific hypotheses which can then be tested using data.

    Deductive reasoning involves moving from general theories to specific observations.

  • Why are stains used in microscopy when making temporary mounts?

    Stains are used when making temporary mounts to provide colour contrast for cellular structures that might otherwise be transparent; this means that the structures can be seen under a microscope.

  • How is a coverslip used during preparation of a temporary mount of cells?

    When making a temporary mount of cells a coverslip is gently lowered over a specimen after liquid and/or stain has been added.

  • Describe how a slide can be viewed using a light microscope.

    A slide can be viewed using a light microscope as follows:

    1. place slide onto microscope stage

    2. lower the low power objective lens towards the stage as far as possible

    3. use the coarse focus to locate the specimen

    4. use the fine focus to bring the specimen into clear view

    5. change the objective lens to increase magnification

    6. repeat steps 3-5 as necessary

  • What is an eyepiece graticule?

    An eyepiece graticule is a transparent scale mounted within the eyepiece lens of a light microscope.

  • How can an eyepiece graticule be used to determine the size of a specimen?

    An eyepiece graticule can be used to determine the size of a specimen by calibrating the graticule using a stage micrometer. This process allows the actual length of each eyepiece graticule unit to be determined, and the eyepiece graticule can be used like a ruler to measure the length of a specimen.

  • What is the formula for calculating the actual size of a specimen?

    The formula for calculating the actual size of a specimen is:

    actual size = image size ÷ magnification

  • What is the formula for calculating magnification?

    The formula for calculating magnification is:

    magnification = image size ÷ actual size

  • True or False?

    50 mm is the same as 5000 μm.

    False.

    There are 1000 μm in 1 mm, so:

    50 mm = 50 000 μm

    5000 μm would be equivalent to 5 mm.

  • Describe how a scale bar can be added to a biological drawing of a specimen viewed using a light microscope.

    A scale bar can be added to a biological drawing as follows:

    1. calibrate the eyepiece graticule and use it to measure the length of the specimen

    2. calculate 20 % of the length of the specimen (or a similar percentage)

    3. draw the specimen according to the rules of biological drawing

    4. use a ruler to draw a line that is 20 % of the length of the drawing

    5. write the actual length represented by the scale bar next to the bar; this should be a whole number

  • True or False?

    Using an eyepiece graticule to measure the size of a specimen is an example of qualitative observation. (NOS)

    False.

    Using an eyepiece graticule to measure the size of a specimen is an example of quantitative observation.

  • How do electron microscopes generate images?

    Electron microscopes generate images by passing a beam of electrons through a specimen (TEM) or by bouncing electrons off the surface of a specimen (SEM).

  • What are the advantages of electron microscopes over light microscopes?

    Advantages of electron microscopes over light microscopes are that they:

    • have higher resolving power

    • can magnify objects many more times (x500 000 compared to x2000)

    • can be used to show the details of internal cellular structures

  • How are specimens prepared using freeze fracture techniques?

    Specimens can be prepared using freeze fracture methods as follows:

    • a specimen is rapidly frozen

    • the frozen tissue is broken apart, or fractured, exposing a surface that can be viewed

  • True or False?

    Freeze fracture techniques can be used to view living specimens.

    False.

    Freeze fracture preparation involves freezing specimens, meaning that anything living would not survive.

  • For what purpose is cryogenic electron microscopy used?

    Cryogenic electron microscope is used for viewing the 3D structures of, e.g.:

    • proteins

    • viruses

    • cell membranes

  • How can fluorescent stains be used in microscopy?

    Fluorescent stains are used in light microscopy; the dyes bind to specific target structures inside cells and then emit light when irradiated, showing where the structures are located within the cell.

  • What is immunofluorescence in microscopy?

    Immunofluorescence uses antibodies with fluorescent dyes attached; the antibodies bind to specific target molecules and the dyes fluoresce when irradiated, showing whether or not, or where, the target molecules are present.

  • Which molecule makes up the genetic material of typical cells?

    The genetic material of typical cells is made from DNA.

  • What is the role of DNA inside cells?

    The role of DNA inside cells is to store the information needed to make proteins.

  • True or False?

    Cell cytoplasm is composed mainly of water.

    True.

    The term cytoplasm refers to the region of a cell between the cell surface membrane and the nucleus. Most of this region is filled with a watery fluid.

  • What is the role of cytoplasm within cells?

    The role of cytoplasm within cells is to provide a medium in which the chemical reactions of cell metabolism can occur.

  • Why is it important that cells are surrounded by a plasma membrane?

    It is important that cells are surrounded by a plasma membrane because it:

    • separates cells from their surroundings

    • allows cells to control which substances enter and leave

    • allow cells to communicate with other cells

  • What is a prokaryotic cell?

    A prokaryotic cell is a type of cell that is small, unicellular and contains no internal membranes.

  • What are the components of a prokaryotic cell?

    Components of a prokaryotic cell include:

    • cell wall

    • plasma membrane

    • cytoplasm

    • naked DNA in a loop

    • 70S ribosomes

    There are other structures found in some prokaryotes.

  • True or False?

    Prokaryotes have multiple chromosomes.

    False.

    Prokaryotes have a single, circular chromosome.

  • What is the role of a prokaryotic cell wall?

    The role of a cell wall in prokaryotes is to maintain cell shape and prevent the cell from bursting due to water intake by osmosis.

  • How do prokaryotic ribosomes compare with eukaryotic ribosomes?

    Prokaryotic ribosomes (70S) are smaller than eukaryotic ribosomes (80S).

  • What are two examples of gram-positive eubacteria?

    Two examples of gram-positive eubacteria are:

    • Bacillus

    • Staphylococcus

  • True or False?

    All prokaryotes have the same cellular features.

    False.

    Prokaryote cell structure varies. While there are some cell structures common to all prokaryotes, other structures are only present in some cells.

  • What are the features common to eukaryotic cells?

    The features common to eukaryotic cells include:

    • plasma membrane

    • compartmentalised cytoplasm

    • 80S ribosomes

    • nucleus

    • mitochondria

    • endoplasmic reticulum

    • Golgi apparatus

    • vesicles, including lysosomes

    • cytoskeleton

  • What is the plasma membrane?

    The plasma membrane is a partially permeable bilayer of phospholipids that surrounds all cells and controls the exchange of materials between the internal and external environment.

  • Define the term compartmentalisation in the context of cells.

    Compartmentalisation refers to the separation of the cell interior into compartments, e.g. the mitochondrial matrix is separated from the rest of the cytoplasm.

  • True or False?

    Eukaryotic cells have 70S ribosomes.

    False.

    Eukaryotes have 80S ribosomes.

    It is prokaryotic cells that have 70S ribosomes.

  • Describe the composition of eukaryotic chromosomes.

    Eukaryotic chromosomes are made of DNA bound to histone proteins.

  • True or False?

    The nuclear membrane provides an impermeable barrier between the nucleus and the cytoplasm.

    False.

    The nuclear membrane contains nuclear pores that allow substances to move between the nucleus and cytoplasm.

  • What is the function of the Golgi apparatus?

    The function of the Golgi apparatus is to modify molecules, e.g. proteins, before packaging them into vesicles for transport to their destination.

  • What are the structures labelled A-C in the image?

    Diagram of a mitochondrion showing labelled parts: A is pointing to the entire organelle, B to the interior of the organelle, and C to the inner folds.

    The structures are:

    • A = mitochondrion (plural mitochondria)

    • B = mitochondrial matrix

    • C = crista (plural cristae) / inner mitochondrial membrane

    Diagram of a mitochondrion showing labelled parts: A is pointing to the entire organelle, B to the interior of the organelle, and C to the inner folds.
  • What is the function of the endoplasmic reticulum?

    The function of the endoplasmic reticulum is as follows:

    • rough endoplasmic reticulum:

      • protein synthesis

      • protein transport

    • smooth endoplasmic reticulum:

      • lipid synthesis

      • production of sex hormones

      • calcium ion storage in muscle cells

  • What are lysosomes?

    Lysosomes are a type of vesicle containing hydrolytic enzymes. They are involved with breaking down:

    • old organelles

    • pathogens during phagocytosis

    • biological molecules stored inside cellular vacuoles

  • What are microtubules?

    Microtubules are hollow fibres made of tubulin protein that form part of the cell's cytoskeleton, providing support and enabling movement of substances around the cell.

  • True or False?

    Microfilaments are made of actin and are part of the cytoskeleton.

    True.

    Microfilaments are made of the protein actin. They, along with the microtubules, form part of the cytoskeleton of cells.

  • What are the process of life that occur in unicellular organisms?

    Process of life that occur in unicellular organisms are:

    • metabolism

    • reproduction

    • homeostasis

    • growth

    • response to stimuli

    • excretion

    • nutrition

    • movement

  • What is homeostasis?

    Homeostasis is the maintenance of internal conditions within tolerable limits.

  • True or False?

    In unicellular organisms cellular vacuoles are involved with homeostasis.

    True.

    Vacuoles known as contractile vacuoles allow unicellular organisms to remove excess water from their cytoplasm, maintaining their water balance.

  • What is excretion?

    Excretion is the disposal of metabolic waste products, including carbon dioxide from respiration.

  • Define the term metabolism.

    A cell's metabolism is all the enzyme-catalysed reactions occurring in a cell, including cell respiration.

  • What is the function of mitochondria in unicellular organisms?

    The function of mitochondria in unicellular organisms is to release energy for cell processes through respiration.

  • How are cilia and flagella involved with the life processes of unicellular organisms?

    Cilia and flagella are involved with movement and responsiveness. They allow unicellular organisms to move around in response to stimuli.

  • Which eukaryotic cell types have a cell wall?

    Eukaryotic cell types with a cell wall are:

    • plant cells

    • fungal cells

  • How do the cell walls of plant cells and fungal cells differ?

    The cell walls of plant and fungal cells differ in that plant cell walls are made of cellulose while fungal cell walls are made of chitin.

  • How does vacuole size and function vary between different eukaryotic cell types?

    Vacuole size and function differs between different cell types as follows:

    • plant cells: large, permanent vacuoles used for carbohydrate storage and cell support

    • animal and fungal cells: small vacuoles with multiple functions, e.g. disposal of waste

  • Which eukaryotic cells contain chloroplasts?

    Chloroplasts are found in plant cells.

  • True or False?

    All eukaryotic cell types contain centrioles.

    False.

    Animal cells contain centrioles but plant ands fungal cells do not.

  • True or False?

    Animal cells may contain cilia or flagella.

    True.

    Animal cells may have cilia or flagella, e.g.:

    • ciliated epithelial cells have cilia

    • sperm cells have a flagellum

  • What are aseptate hyphae?

    Aseptate hyphae are strands of fungal cells with no cross-walls to separate the cells. This means that the hyphae contain continuous cytoplasm and multiple nuclei.

  • How are skeletal muscle cells atypical?

    Skeletal muscle cells are atypical in that they:

    • are long

    • contain multiple nuclei

    • contain proteins that allow them to contract and relax

  • How are red blood cells atypical?

    Red blood cells are atypical in that they:

    • contain haemoglobin

    • have no nucleus

    • have a biconcave disc shape

  • True or False?

    Phloem sieve tubes have perforated end walls and normal cell contents.

    False.

    Phloem sieve tube cells do have perforated end walls, but they have reduced cell contents, e.g. less cytoplasm.

  • What type of eukaryotic cell is shown in the image?

    Close-up view of plant cells under a microscope showing green chloroplasts and rectangular cell walls. The cells are tightly packed in a grid-like pattern.

    The cell type shown in the image is a plant cell. This is because the light micrograph shows cells with a regular shape that have visible green chloroplasts.

    Close-up view of plant cells under a microscope showing green chloroplasts and rectangular cell walls. The cells are tightly packed in a grid-like pattern.

    Image credit: and3k and caper437, via Wikimedia Commons

  • Which cellular organelle is shown in the image?

    A rounded organelle with an outer and inner membrane.

    The organelle in the image is a mitochondrion. It is recognisable due to its internal cristae.

    A rounded organelle with an outer and inner membrane.
  • Which cellular organelles are labelled A-C in the image?

    Micrograph of a cell with labelled parts. A points to an elongated membrane-bound structure, B to the largest structure in the cell, and C to multiple dark circular dots.

    Structures A-C are:

    • A = (rough or smooth) endoplasmic reticulum

    • B = nucleus

    • C = lysosome / vesicle

    Sometimes images of cells are not easy to interpret, meaning that more than one reasonable answer may be permitted.

    Micrograph of a cell with labelled parts. A points to an elongated membrane-bound structure, B to the largest structure in the cell, and C to multiple dark circular dots.
  • What type of cell is shown in the electron micrograph?

    Electron microscope image of a single, rod-shaped bacterium with multiple long, thin flagella extending from its body. Scale bar shows 1 micrometer.

    The cell shown in the image is a bacterial cell. It is recognisable by the presence of flagella, as well as its small size.

    Electron microscope image of a single, rod-shaped bacterium with multiple long, thin flagella extending from its body. Scale bar shows 1 micrometer.

    Image credit: HANS G. SCHLEGEL, via Wikimedia Commons

  • Which cellular organelles are labelled A-C in the image?

    Electron microscope image showing a cell with labelled structures: 'A' (mitochondrion), 'B' (nuclear membrane), 'C' (ribosomes).

    The organelles are:

    • A = mitochondrion / lysosome

    • B = nuclear membrane

    • C = cytoplasm / cytosol / ribosome

    Sometimes real images are not easy to interpret, meaning that more than one reasonable answer may be permitted.

    Electron microscope image showing a cell with labelled structures: 'A' (mitochondrion), 'B' (nuclear membrane), 'C' (ribosomes).

    Image credit: Nukleolus, via Flickr

  • What are the conventions of biological drawing?

    The conventions of biological drawing include:

    • Drawings should be on plain white paper

    • Lines should be clear, single lines with no sketching

    • No shading

    • The drawing should take up as much of the space as possible

    • The drawing should show visible structure with proper proportions

    • Label lines should be drawn with a ruler, should not have arrows and should not cross

    • Title and annotations should be added

  • True or False?

    Shading should be used in biological drawings.

    False.

    No shading should be used in biological drawings.

  • True or False?

    Label lines in biological drawings should have arrowheads.

    False.

    Label lines in biological drawings should not have arrowheads, but instead the end of each line should touch the relevant part of the drawing.

  • What additional information should be included in the annotations of cell drawings?

    The functions of organelles and cells should be included as part of the annotations in cell drawings.