Section 1: Cell Structure Flashcards
What is the function of a plasma membrane?
The function of the plasma membrane is to regulate the movement of substances into and out of the cell. It also has receptor molecules on it, which allow it to respond to chemicals like hormones.
What is magnification?
Magnification is how much bigger the image is than the specimen (the sample you’re looking at).
What is the formula for magnification?
Magnification = Image size
—————-
Actual size
What is resolution and give an example.
Resolution is how detailed the image is. More specifically, it’s how well a microscope distinguishes between two points that are close together. If a microscope lens can’t separate two objects, then increasing the magnification won’t help.
For example, when you look at a car in the dark that’s a long way away you see the two headlights as one light. This is because your eyes can’t distinguish between the two points at a distance - your eyes produce a low resolution image. When the car gets a bit closer you can see both headlights - a higher resolution image.
What are the different types if microscope?
Light microscopes, laser scanning confocal microscopes and electron microscopes.
Describe light microscopes.
They use light. They have a lower resolution than electron microscopes. They have a maximum resolution of about 0.2 micrometers. So they’re usually used to look at whole cells or tissues. The maximum useful magnification is about x1500.
Describe laser scanning confocal microscopes.
These are a special type of light microscope that use laser beams (intense beams of light) to scan a specimen that’s usually tagged with fluorescent dyes.
A laser beam is focused through a lens which is aimed at a beam splitter. This splits the beam and some of the light is directed to the specimen. When the laser hits the dyes it causes them to give off fluorescent light. This light is then focused through a pinhole onto a detector. The detector is hooked up to a computer, which generates an image. The pinhole means that any out-of-focus light is blocked, so these microscopes produce a much clearer image than a normal light microscope.
These microscopes can be used to look at objects at different depths in thick specimens. Multiple images produced by the microscope can be combined by the computer to generate 3D images of a specimen.
Describe electron microscopes.
Electron microscopes use electrons instead of light to form an image. They have a higher resolution than light microscopes so give more detailed images.
What are the types of electron microscope?
Transmission electron microscope (TEM) and scanning electron microscope (SEM)
Describe transmission electron microscopes.
TEMs use electromagnets to focus a beam of electrons, which is then transmitted through the specimen to produce 2D images. Denser parts of the specimen absorb more electrons, which makes them look darker on the image you end up with.
TEMs are good because they provide high resolution images, so they can be used to look at very small organelles, e.g. ribosomes. They can also be used to look at the the internal structures of organelles in detail. But specimens viewed on TEMs need to he quite thinly sliced. The angle at which specimens are cut can affect how they appear.
Describe scanning electron microscopes.
SEMs scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image. The images produced show the surface of the specimen and can be 3D but they give lower resolution than TEMs.
Describe protein production
There are a variety of organelles involved in protein production. Each one has a different role. Proteins are made at the ribosomes - the ribosomes on the rough endoplasmic reticulum (RER) make proteins that are excreted or attached to the cell membrane, whereas the free ribosomes in the cytoplasm make proteins that stay in the cytoplasm.
New proteins produced at the RER are folded and processed (e.g. sugar chains are added) in the RER. Then they’re transported from the RER to the Golgi apparatus in vesicles. At the Golgi apparatus, the proteins may undergo further processing (e.g. sugar chains are trimmed or more are added). The proteins enter more vesicles to be transported around the cell. E.g. glycoproteins (found in mucas) move to the cell surface and are secreted.
What are prokaryotic and eukaryotic cells?
There are two main types of organism - eukaryotes and prokaryotes. Prokaryotic organisms are prokaryotic cells (i.e. they’re single celled organisms) and eukaryotic organisms are made up of eukaryotic cells. Both types of cells contain organelles. Eukaryotic cells are complex and include all animal and plant cells. Prokaryotic cells are smaller and simpler, e.g. bacteria.
What are organelles?
Organelles are parts of cells. Each one has a specific function. If you examine a cell through an electron microscope, you can see its organelles and the internal structure of most of them - this is known as the cell ultrastructure.
Describe the features of an animal cell.
An animal cell contains a plasma membrane, rough endoplasmic reticulum, a nucleolus, a nucleus, smooth endoplasmic reticulum, lysosomes, ribosomes, a nuclear envelope, a Golgi apparatus, cytoplasm and mitochondria.
Describe the features of a plant cell.
A plant cell contains a plasma membrane, rough endoplasmic reticulum, a nucleolus, a nucleus, smooth endoplasmic reticulum, lysosomes, ribosomes, a nuclear envelope, a Golgi apparatus, cytoplasm, mitochondria, a vacuole, a cellulose cell wall and chloroplasts.
How do animal cells and plant cells differ?
Plant cells have all the same organelles as animal cells, but with a few added extras;
- a cell wall with plasmodesmata (‘channels’ for exchanging substances between adjacent cells).
- a vacuole (compartment that contains cell sap).
- chloroplasts (the organelles involved in photosynthesis).
Describe the plasma membrane and explain its function.
The plasma membrane is the membrane found on the surface of animal cells and just inside the cell wall of plant cells and prokaryotic cells. It’s made mainly of lipids and proteins.x
The function of the plasma membrane is to regulate the movement of substances into and out of the cell. It also has receptor molecules on it, which allow it to respond to chemicals like hormones.
Describe the cell wall and explain its function.
The cell wall is a rigid structure that surrounds plant cells. It’s made mainly of the carbohydrate cellulose.
The function of the cell wall is to support plant cells.
Describe the nucleus and explain its function.
The nucleus is a large organelle surrounded by a nuclear envelope (double membrane), which contains many pores. The nucleus contains chromatin (which is made from DNA and proteins) and often a structure called the nucleolus.
The function of the nucleus it that it controls the cell’s activities (by controlling the transcription of DNA). DNA contains instructions to make proteins. The pores allow substances (e.g. RNA) to move between the nucleus and the cytoplasm. The nucleolus makes ribosomes.
Describe a lysosome and explain its function.
A lysosome is a round organelle surrounded by a membrane, with no clear internal structure.
The function of a lysosome is that it contains digestive enzymes. These are kept separate from the cytoplasm by the surrounding membrane, and can be used to digest invading cells or to break down worn out components of the cell.
Describe a ribosome and explain its function.
A ribosome is a very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum. It’s made up of proteins and RNA. It’s not surrounded by a membrane.
The function of the ribosome is that it is the site where proteins are made.
Describe the rough endoplasmic reticulum (RER) and explain its function.
The RER is a system of membranes enclosing a fluid-filled space. The surface is covered with ribosomes.
The function of the RER is to fold and process proteins that have been made at the ribosomes.
Describe the smooth endoplasmic reticulum (SER) and explain its function.
The SER is similar to the RER, but with no ribosomes.
The function of the SER is to synthesise and process lipids.
