Cell Biology and Techniques Quiz

Microscopy

• Microscopes magnify objects, making them appear larger than they are. This allows observation of objects too small to be seen with the naked eye.
• There are two basic types of microscopes: simple and compound.
• Simple microscopes are early types, consisting of a single lens, such as a magnifying glass.
• Compound microscopes, which contain more than one lens, are parfocal(still focused when objectives are switched). Research microscopes use transmitted light, creating an inverted image and commonly magnify up to 400X, ideal for transparent specimens. Dissecting microscopes are parfocal and have a single objective that allows for a virtual image (same as the actual object) useful with solid objects and magnification up to 30X.
• Parts of a microscope include: Ocular (magnifies 10X), Objective Lenses (vary in magnification: low 4x, medium 10x, high 40x), Revolving Nosepiece (holds objectives), Course Focusing Knob(focuses the object on low power), Fine Focusing Knob(clears image), Iris Diaphragm (regulates light), Light Source.

The Cell Theory

• Early humans were unable to explain how life arose. Early scientists and doctors had theories about life appearing out of non-living materials.
• Spontaneous generation stated that life could arise from non-living matter. This theory was disproven by Francesco Redi (1668) and Louis Pasteur (1864) through experiments using sealed vessels.
• The Cell Theory applies to all living things, except prions & viruses. It is fundamental to biology, beginning with the observations of Aristotle, Robert Hooke (1665, who coined the term "cell"), and Antoni van Leeuwenhoek.

Cell Theory details.

• The Cell Theory states that
  1. All living things are made of one or more cells and/or substances produced by these cells.
  2. All life functions take place within the cell, making them the smallest unit of life.
  3. All cells are produced by the division of pre-existing cells.

Imaging and Staining Techniques

• Microscope observation is affected by contrast (showing differences between structures) and resolution (showing detail). Contrast can be improved with staining techniques (e.g., iodine, methylene blue).
• New technologies allow improved imaging in research, like fluorescence microscopy, which uses ultraviolet light for glowing samples, or confocal technology for 3-D images or electron microscopes. Electron microscopes use beams of electrons, with two types: Transmission Electron Microscopes (TEM) and Scanning Electron Microscopes (SEM). TEMs have a high magnification (up to 100,000 times). SEMs produce 3-D images in a vacuum, with a magnification up to 300,000.

Cell Research at the Molecular Level

• Advances in technology, like Scanning Tunneling Microscopes (STM) and Atomic Force Microscopes (AFM), are used to image molecules.
• Gene mapping using the Human Genome Project allowed understanding and mapping of the location and function of genes in chromosomes.
• Biochemists & microbiologists showed that DNA contains genes which direct all cell activities and traits.

The Cell as an Efficient, Open System

• Cells are open systems, exchanging matter and energy with their surroundings.
• Cells acquire nutrients and excrete waste.
• Cells carry out all life processes.
• Two types of cells exist: prokaryotic cells (lack nuclei, DNA floats in cytoplasm, e.g., bacteria) and eukaryotic cells(have nuclei, DNA is packaged into chromosomes, e.g., plants, animals).

Cell Structures

• The five main structures of a plant cell are: Cell wall (provides strength & support, found in plant cells, bacteria, and protists, made of cellulose), Cell membrane (protective barrier, semi-permeable, maintains balance or equilibrium), Nucleus (directs cellular activities, has DNA, a porous membrane & nucleolus), Cytoplasm (gel-like substance with organelles), and Organelles (tiny "organs" within the cell which have different functions).
• Examples of organelles include: Mitochondria (site of cellular respiration), Endoplasmic Reticulum (smooth ER - site of fat/lipid & steroid production, rough ER - site of protein synthesis), Ribosomes (site of protein synthesis, take amino acids to make protein), Golgi Apparatus (stores proteins secreted outside the cell), Lysosomes (digest bacteria/damaged proteins, found in animal cells only, "suicide sac"), Vacuoles & Vesicles (storage of nutrients and water), Chloroplasts (site of photosynthesis).
• Plant cells also have a rigid cell wall, and a large central vacuole for water storage.

Plant Transport

• Plants transport water and nutrients from the roots to the leaves.
• This process is aided by cohesion (attraction between water molecules-occurs because water is a polar molecule), adhesion (attraction between water and other substances-i.e. xylem wall), root pressure, and transpiration pull (water lost by evaporation through stomata, which pulls water up).
• Plants have different tissues for gas exchange, including: dermal tissue which is the outermost layer (e.g. cuticle, stomata), ground tissue(inside the dermal tissue), vascular tissue which transports substances between the roots and shoots (xylem and phloem).

Plant Responses to Stimuli

• Tropisms are responses that plants have to stimuli, such as light or gravity.
• Phototropism is a plant's response to light, and it can be either positive (growing towards the light - e.g. leaves and stems) or negative (growing away from the light -e.g. roots).
• Gravitropism is a plant's response to gravity, and positive gravitropism occurs when there is growth in the same direction as gravity (e.g.roots), whereas negative gravitropism occurs when there is growth in the opposite direction (e.g. stem).
• Other factors which influence a plant's growth include temperature, touch (e.g. tendrils such as ivy). and length of daylight hours.

Other Applications

• Membrane technologies are useful for creating liposomes for safer drug delivery and dialysis to remove waste from the blood when kidneys fail. There are two types of dialysis: peritoneal and hemodialysis.

Starch-Glucose & Iodine-Starch Tests

• For the starch-glucose test, a solution of starch and glucose placed in dialysis tubing and then placed in water, may result in a color change as the substance diffuses, depending on the materials used for the test.
• If an iodine-starch test uses a solution of starch and glucose placed in dialysis tubing and then immersed in a yellow iodine solution, the color change depends on the ability of the substances used in the test to pass through the semi-permeable membrane of the dialysis tubing.