Cell Structure & Organisation (Edexcel A Level Biology (A) SNAB): Flashcards
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- FrontCell Theory
Define cell theory.
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Define cell theory.
Cell theory is the universally accepted idea that all living organisms are made of cells, first proposed by Schleiden and Schwann.
State the three main ideas of cell theory.
All living organisms are made of one or more cells.
Cells are the basic functional unit of life.
New cells are produced from pre-existing cells.
Who is credited with first viewing and naming cells?
Robert Hooke, who used the term 'cell' to describe the structures he saw.
Which scientists proposed that all living organisms are made of cells?
Schleiden and Schwann, in 1837.
Give four features common to the cells of all living organisms.
A cell surface membrane.
Cytoplasm.
DNA.
Ribosomes.
Define ultrastructure.
Ultrastructure refers to the detailed internal structure of a cell, as seen under an electron microscope.
What does it mean that cell theory is a unifying concept in biology?
It is universally accepted.
It applies to all living organisms, linking ideas across biology.
Why was the development of the microscope important for cell theory?
Cells are too small to see with the naked eye.
Microscopes powerful enough to view individual cells were needed before cell theory could be developed.
According to cell theory, all new cells are produced from cells.
According to cell theory, all new cells are produced from pre-existing cells.
True or False?
Cell theory states that cells are the basic functional unit of living organisms.
True.
This is one of the three main ideas of cell theory.
How do prokaryotic and eukaryotic cells differ beyond their common features?
Prokaryotic cells have no internal membranes and smaller ribosomes.
Eukaryotic cells have membrane-bound organelles and larger ribosomes.
True or False?
Cell theory was accepted before microscopes were invented.
False.
Cell theory could only be developed after microscopes became powerful enough to view cells.
Define organelle.
An organelle is a specialised structure within a cell that carries out a particular function; many are membrane-bound.
What is the function of the nucleus?
It contains the cell's DNA as chromatin.
It is the site of transcription, and its nucleolus makes ribosomes.
What is the function of the mitochondria?
They are the site of aerobic respiration.
Their matrix contains the enzymes that produce ATP.
What is the role of the nucleolus?
It is the site of ribosome production.
What is the function of a lysosome?
It contains hydrolytic enzymes.
It breaks down waste materials such as worn-out organelles, and is used in apoptosis.
Give three structures found in plant cells but not animal cells.
A cellulose cell wall.
A large permanent vacuole.
Chloroplasts.
What is the difference between rough and smooth endoplasmic reticulum?
Rough ER is covered in ribosomes and processes proteins.
Smooth ER has no ribosomes and makes lipids, carbohydrates and steroids.
What is the role of the rough endoplasmic reticulum in protein production?
Ribosomes on its surface make proteins that are then passed into its lumen.
Here the proteins are folded and processed.
What is the role of the Golgi apparatus in protein production?
It modifies proteins received from the RER.
It then packages them into vesicles for secretion or delivery.
Describe the pathway of a secreted protein through the cell.
Made on ribosomes of the RER and processed.
Carried in a vesicle to the Golgi apparatus, modified, then released in a vesicle that fuses with the cell surface membrane.
Proteins are transported between organelles, and out of the cell, inside membrane-bound .
Proteins are transported between organelles, and out of the cell, inside membrane-bound vesicles.
True or False?
Free ribosomes in the cytoplasm make proteins that are exported from the cell.
False.
Free ribosomes make proteins that stay in the cytoplasm — proteins for export are made on the RER.
Define prokaryotic cell.
A prokaryotic cell is a small cell with no nucleus and no membrane-bound organelles, such as a bacterium.
How does the genetic material of a prokaryote differ from a eukaryote?
Prokaryotes have a single circular chromosome free in the cytoplasm.
It is not associated with proteins (histones), and there is no nucleus.
How do prokaryotic ribosomes differ from eukaryotic ribosomes?
Prokaryotic ribosomes are smaller (70S).
Eukaryotic ribosomes are larger (80S).
What is the prokaryotic cell wall made of?
Murein, a glycoprotein also known as peptidoglycan.
Define plasmid.
A plasmid is a small loop of DNA, separate from the main chromosome, found in many prokaryotic cells.
Give three structures found in some, but not all, prokaryotic cells.
Any three of:
Plasmids
A capsule
Flagella or pili
What is the function of a flagellum in a prokaryote?
It enables the cell to move.
State two key differences between prokaryotic and eukaryotic cells.
Prokaryotes have no nucleus; eukaryotes have one.
Prokaryotes have no membrane-bound organelles; eukaryotes do.
The cell wall of a prokaryote contains the glycoprotein .
The cell wall of a prokaryote contains the glycoprotein murein.
True or False?
Size is a valid structural difference between prokaryotic and eukaryotic cells.
False.
Size is not a structural feature — a structural difference should refer to features such as the nucleus or organelles.
True or False?
All prokaryotic cells have a capsule and flagella.
False.
These structures are found in many but not all prokaryotic cells.
What is the function of a plasmid in a bacterium?
It carries extra genes, such as those for antibiotic resistance.
These can be passed between bacteria.
List the levels of organisation from cell to organism.
Cell → tissue → organ → organ system → organism.
Define tissue.
A tissue is a group of similar cells that work together to perform a particular function.
Define organ.
An organ is a group of different tissues that work together to perform a particular function.
Define organ system.
An organ system is a group of organs that work together to perform a particular function.
Define specialised cell.
A specialised cell is a cell adapted to carry out a particular function, such as a red blood cell transporting oxygen.
How is a red blood cell specialised for its function?
It is specialised to transport oxygen.
Give an example of a tissue and its function.
Muscle tissue is made of muscle cells.
It contracts to move parts of the body.
Explain how the heart is an example of an organ.
It is made of several tissues working together — cardiac muscle, blood vessel and connective tissue.
Together they let it pump blood around the body.
Give an example of an organ system and the organs in it.
The digestive system includes the stomach, pancreas, small intestine and large intestine.
Together they digest food and absorb nutrients.
A group of different tissues working together to perform a function is called an .
A group of different tissues working together to perform a function is called an organ.
True or False?
A tissue is made of only one type of cell.
False.
A tissue is a group of cells working together, but it can contain more than one cell type.
How do the heart and blood vessels form an organ system?
They are organs that work together as the circulatory system.
This system circulates blood around the body.
How does a light (optical) microscope produce an image?
Light is directed through a thin specimen on a slide.
It is focused through lenses so an image is visible through the eyepiece.
Why should you start with the low power objective lens?
It is easier to find the specimen in the field of view.
It also helps prevent damage to the lens or coverslip.
Why must a specimen be a thin layer of cells?
So that light can pass through it.
This allows the structures to be seen clearly.
Why is a coverslip pressed down gently onto a specimen?
To remove air bubbles.
Air bubbles would otherwise obscure the view of the cells.
Why are stains used when preparing specimens?
Many cell structures are transparent or hard to distinguish.
Stains are absorbed by different structures, making them visible and adding contrast.
What does methylene blue stain?
It stains animal cell nuclei blue.
What does iodine stain in plant cells?
It stains starch-containing material blue-black.
Define differential staining.
Differential staining is the use of multiple dyes so that several different tissues in a specimen show up distinctly.
Give three conventions for a biological drawing.
Use clear single lines with no shading or sketching.
Include a title and the magnification.
Use label lines drawn with a ruler that do not cross or have arrowheads.
What is the difference between a cellular drawing and a plan drawing?
A cellular drawing shows individual cells, made at high magnification.
A plan drawing shows the arrangement of tissues at low magnification, with no individual cells.
When making a biological drawing you should only draw structures that are actually .
When making a biological drawing you should only draw structures that are actually visible.
True or False?
Biological drawings should be shaded to show depth.
False.
Biological drawings use clear single lines with no shading.
Define magnification.
Magnification is how many times larger the image of a specimen is compared with its actual size.
State the equation linking magnification, image size and actual size.
magnification = image size ÷ actual size
How do you calculate the total magnification of a light microscope?
Multiply the eyepiece lens magnification by the objective lens magnification.
Why must image and actual size be in the same units before a magnification calculation?
Otherwise the calculation gives the wrong answer.
For example, both should be converted to µm before dividing.
An image of a cell is 30 mm across and has been magnified ×3000. Calculate the actual size in µm.
actual size = image size ÷ magnification
= 30 ÷ 3000 = 0.01 mm = 10 µm
How do you convert a measurement in mm to µm?
Multiply by 1000, because there are 1000 µm in 1 mm.
Define eyepiece graticule.
An eyepiece graticule is a small engraved scale placed in the eyepiece that acts as a ruler in the field of view.
Why must an eyepiece graticule be calibrated?
It has no fixed units.
Its scale must be calibrated against a stage micrometer, and recalibrated at each magnification.
What is a stage micrometer used for?
It is a slide with an engraved scale of known size.
It is used to calibrate the eyepiece graticule.
If 40 graticule divisions line up with 0.01 mm on the stage micrometer, what is one graticule division worth?
0.01 mm = 10 µm across 40 divisions.
10 ÷ 40 = 0.25 µm per division.
The magnification equation is magnification equals image size divided by size.
The magnification equation is magnification equals image size divided by actual size.
True or False?
An eyepiece graticule needs recalibrating each time the magnification is changed.
True.
The graticule stays the same apparent size, so its real-world value changes with magnification and must be recalibrated.
Define resolution.
Resolution is the ability to distinguish between two separate points as distinct.
Why does an electron microscope have a higher resolution than a light microscope?
Electrons have a much shorter wavelength than visible light.
This lets the microscope distinguish points that are much closer together.
Why is the resolution of a light microscope limited?
It is limited by the wavelength of light.
The wavelength of visible light is too long to resolve very small structures.
Why is there no point magnifying an image beyond the microscope's resolution?
Magnifying further just makes an unclear image bigger.
The two points still cannot be told apart, so no extra detail is seen.
How does a transmission electron microscope (TEM) form an image?
A beam of electrons is transmitted through a thin specimen.
Denser parts absorb more electrons and appear darker, giving a high-resolution 2D image.
How does a scanning electron microscope (SEM) form an image?
A beam of electrons is scanned across the specimen and bounces off the surface.
The reflected electrons form a 3D image of the surface.
What is the main difference between the images from a TEM and an SEM?
A TEM gives a high-resolution 2D image of internal structures.
An SEM gives a lower-resolution 3D image of the surface.
How can you tell whether a micrograph was taken with a TEM or an SEM?
If internal structures are visible, it is a TEM.
If the image looks 3D and shows the surface, it is an SEM.
Why must specimens for electron microscopy be dead?
The specimen is placed in a vacuum and treated during preparation.
So the image is only a snapshot of the cell at one moment.
A transmission electron microscope produces a image, whereas a scanning electron microscope produces a 3D image.
A transmission electron microscope produces a 2D image, whereas a scanning electron microscope produces a 3D image.
True or False?
An SEM has a higher resolution than a TEM.
False.
A TEM has the higher resolution; an SEM produces lower-resolution 3D surface images.
Define electron micrograph.
An electron micrograph is an image produced by an electron microscope.
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