Cell Structure Flashcards
What is a cell?
A cell is the basic unit of all living organisms. It is surrounded by a cell surface membrane and contains genetic material (DNA) and cytoplasm containing organelles.
What is an organelle?
A functionally and structurally distinct part of the cell, e.g. a ribosome or mitochondrion.
What is a nucleus?
A nucleus is a relatively large organelle found in eukaryotic cells but absent from prokaryotic cells. The nucleus contains the cells DNA and therefore controls the activities of the cell. It is surrounded by two membranes which together form the nuclear envelope. As DNA is in the nucleus it is protected from degradation from enzymes.
What is a eukaryote?
Eukaryote is an organism whose cell contains a nucleus and other membrane-bound organelles.
What is a prokaryote?
An organism whose cells do not contain a nucleus or any other membrane-bound organelles.
What are the two types of microscopes?
There are two fundamentally different types of microscope: the light microscope and the electron microscope.
Which form of radiation do electron microscopes use?
The electron microscope uses electrons as a source of radiation.
Which form of radiation do light microscopes use?
The light microscope uses light as a source of radiation.
Describe the unit millimeter.
Millimeter (mm) is 10-3.
Describe the unit micrometer.
Micrometer (μm) is 10-6.
Describe the unit nanometer.
nanometer (nm) is 10-9.
Define the cell surface membrane.
Sometimes called plasma membrane. A very thin membrane (about 7nm in diameter) surrounding all cells. It is partially permeable and controls the exchange of materials between the cell and its environment.
Define chromatin.
The material of which chromosomes are made, consisting of RNA, visible as patches or fibers within the nucleus when stained. Chromatin=DNA and its associated proteins.
Define chromosomes.
Chromosomes are in the nucleus of the cells of eukaryotes, a structure made of tightly coiled chromatin (DNA, proteins and RNA) visible during cell division. The term circular DNA is now also commonly used for the circular strand of DNA present in prokaryotic cells.
Define nucleolus.
A small structure, one or more of which is found inside the nucleus. The nucleolus is usually visible as a densely stained body (densest region). Its function is to manufacture ribosomes using the information in its own DNA. Site of ribsomal RNA (rRNA) synthesis.
Define protoplasm.
All the living material inside a cell (cytoplasm+nucleus).
Define cytoplasm.
The contents of a cell, excluding the nucleus.
Define mitochondrion.
Mitochondrion is the organelle in eukaryotes in which aerobic respiration takes place. It is the most numerous organelle seen with a light microscope.
Define cell wall
A wall surrounding prokaryotes, plant and fungal cells. the wall contains a strengthening carbohydrate material cellulose which protects the cell from mechanical damage, supports it and prevents it from bursting by osmosis if the cell is surrounded by a solution with a higher water potential.
Thick rigid layer
Cell wall is freely permeable because there are spaces/gaps between fibres.
Cell wall limits cell size.
What is the average size of a bacteria cell?
An average bacteria cell is about 1 µm across.
What is the size of a ribosome?
One of the smallest structures you will study in the syllabus is a ribosome which is only about 25nm in diameter.
What is a photomicrograph?
A photomicrograph is a photograph of a specimen as seen with a light microscope.
Why are plant cells sometimes not stained?
The plant cells have not been stained because the chloroplast contain the green pigment chlorophyll and are easily visible without staining.
What is plasmodesma?
Plasmodesma (plural plasmodesmata) are a pore-like structure found in plant cell walls. Plasmodesmata of neighboring plant cells line up to form tube-like pores through cell walls, allowing the controlled passage of materials from one cell to the other. The pores contain ER and are lined with the cell surface membrane.
Plasmodesmata are strands of cytoplasm passing through channels. They contain little to no cell wall.
Function: allow substances to pass from cell to cell without passing through cell walls.
Plasmodesmeta are small in size so do not allow large organelles to pass through.
Define a vacuole.
An oraganelle found in eukaryotic cells, a large permanent central vacuole is a typical feature of plant cells, where it has a variety functions, including storage of biochemicals such as salts, sugars and waste products. Temporary vacuoles such as phagocytic vacuoles may form in the animal cells.
It pushes chloroplasts to the edge of cells so that chloroplasts are in a better position to capture sunlight.
Define tonoplasts.
The partially permeable membrane that surrounds plant vacuoles. It is also made up of phospholipid bilayer.
Define chloroplasts.
An organism bounded by an envelope (i.e. two membranes), in which photosynthesis takes in eukaryotes. Found mainly in the leaves. They are relatively large so can easily be seen with a light microscope.
Define photosynthesis.
The production of organic substances from inorganic ones, using energy from light.
Define Granum.
Grana (singular:granum) stacks of membrane inside a chloroplast. It is possible to see grana with a light microscope. These are the parts of the plants that contain chlorophyll the green pigment which absorbs light during the process of photosynthesis.
Define magnification.
The number of times larger an image of an object is than the real size of the object.
Magnification=Image size/Actual (real) size of the object.
1. Convert
2. Substitute
3. Calculate
magnification should always be whole number and x sign at front.
