AS - Unit 1 - Cells Flashcards
What is the maximum magnification of a light microscope?
X1500
What is the definition of magnification?
The degree to which the size of an image is larger than the object itself.
What is the definition of resolution?
The degree to which it is possible to distinguish between two objects that are very close together. The higher the resolution, the greater the detail you can see
What is the highest resolution of the light microscope?
200 nm
What kind of organism can you see under a light microscope?
A living one
What is an artefact?
When a microscope specimen is distorted during the preparation process and therefore isn’t an accurate representation
How do you prepare a specimen for a light microscope?
- Staining - coloured stains are applied to allowed the specimen to be seen.
- Sectioning - specimens are embedded in wax, thin sections are then cut without distorting the structure of the specimen
What is the order of the units of measurement?
Metre (m) Decimetre (dm) Centimetre (cm) Millimetre (nm) Micrometre (um) Nanometre (nm)
What is the highest resolution for the human eye?
100 um
What is the highest resolution for the electron microscope?
0.20nm
How do you calculate magnification and size of a specimen?
Actual size X magnification
What are the two types of electron microscope?
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
How do TEM’s work??
The electron beam passes through a very thin prepared sample
Electrons pass through the denser parts of the sample less easily giving some contrast in the final image
How does an SEM work??
The electron beam is directed onto a sample
The electrons don’t pass through the specimen they are ‘bounced off’ the sample
Which electron microscope produces a 3D image??
A scanning electron microscope (SEM)
What is the max magnification of a TEM microscope??
X500 000
What is the max magnification of an SEM?
X100 000
Give 3 advantages of the electron microscope?
The resolution is 0.1nm (2000X better than a light microscope)
Can be used to produce detailed images of the organelles inside cells
SEM produces 3D images that can reveal the detail of contours and cellular or tissue arrangements
Give 3 limitations of the electron microscope
Samples have to be dead
Expensive
Preparing samples for and using the electron microscope requires a high degree of skill and training
Give the definition of staining (referring to microscopy)
Refers to any process that helps to reveal or distinguish difference features
What do electron microscope images look like?
Black and white
What is division of labour?
Each organelle has a specific role to play in the function of the cell, all the different organelles work together in a cell, each contributing it’s part to the survival of the cell
What is the cytoskeleton?
A network of fibres made of protein that keep the cell’s shape stable by providing an internal framework
Some fibres are called actin filaments, what role do they play in the cell?
Actin filaments move against each other and move some organelles around inside cells
What are microtubules?
They are cylinders inside the cell that are about 25nm in diameter. They are made of a protein called tubulin. They are used to move a microorganism through a liquid or to waft a liquid past the cell. They move chromosomes during mitosis, vesicles from the er to the Golgi. They use ATP to drive these movements
What is a eukaryote?
A cell with a nuclei
What are flagella or cilia?
Hair-like extensions that stick out from the surface of cells. Each one is made up of a cylinder that contains 9 microtubules arranged in a circle.
What are prokaryotes?
Cells without a nuclei
What are vesicles?
Membrane-bound sacs found in cells. They are used to carry many different substances around the cell
What does the vacuole do in a plant cell??
Maintains cell stability
What is a vacuole filled with and what is its purpose?
Water and solutes, to maintain cell stability and push the cytoplasm against the cell wall making the cell turgid. This helps to support the plant
What are plant cell walls made from??
Cellulose
What is the structure of the nucleus?
Largest organelle
Surrounded by a nuclear envelope
What is the function of the nucleus?
Houses nearly all the cell’s genetic material
What is the structure of endoplasmic reticulum?
Series of flattened, membrane-bound sacs
They are attached to the outer nuclear membrane
Rough ER is studded with ribosomes
Smooth ER does not have ribosomes
What is the function of the endoplasmic reticulum
Rough ER - transports proteins that were made on the attached ribosomes
Smooth ER - involved in making lipids that the cell needs
What is the structure of the Golgi apparatus?
Stack of membrane-bound, flattened sacs
What is the function of the Golgi apparatus?
Receives proteins from the ER and modifies them into vesicles which can then be transported to the surface of the cell so it can be secreted
What is the structure of the mitochondria?
Spherical or sausage-shaped
Two membranes separated by a fluid-filled space
What is the function of the mitochondria?
The site where ATP is produced during respiration
What is the structure of the chloroplasts?
Found only in plant cells and the cells of some protoctists
Two membranes separated by a fluid filled space
What is the function of chloroplasts?
The site of photosynthesis in plant cells
What is the structure of lysosomes?
Spherical sacs surrounded by a single membrane
What is the function of lysosomes?
Break down materials e.g. White blood cell lysosomes help to break down invading microorganisms
What is the structure of the ribosomes?
Two subunits
What is the function of ribosomes?
Site of protein synthesis in the cell, they act as an assembly line where coded information from the nucleus is used to assemble proteins from amino acids
What is the structure of the centrioles??
Small tubes of protein fibres
What is the function of the centrioles?
Take part in cell division, form fibres known as the spindle which move chromosomes during nuclear division
What does the term organelle mean?
Refers to the particular structure of a cell that has a specialised function. Some organelles are membrane-bound, others are not. All perform a particular role in the life processes of the cell
Where are the instructions the make hormones??
In the DNA in the nucleus
Give the 9 steps of protein synthesis
- mRNA copy of the instructions for insulin is made in the nucleus
- mRNA leaves through the nuclear pore
- mRNA attaches to a ribosome on the rough ER, ribosome reads the instructions to assemble the protein
- Insulin molecules are ‘pinched off’ in vesicles and travel towards the Golgi
- Vesicle fuses with Golgi apparatus
- Golgi processes and packages insulin molecules ready for release
- Packaged insulin molecules are ‘pinched off’ in vesicles from Golgi and move towards cell surface membrane
- Vesicle fuses with cell surface membrane
- Cell surface membrane opens to release insulin molecules outside
Give 7 features of prokaryotes
Only have one membrane
Surrounded by a cell wall
Contain ribosomes that are smaller than eukaryotic ribosomes
DNA in the form of a single loop
DNA is not surrounded by a membrane
ATP production takes place in specialised infolded regions of the cell surface membrane called mesosomes
Some prokaryotic cells have flagella
What is the phospholipid bi-layer?
The basic structural component of plasma membranes. It consists of two layers of phospholipid molecules. Proteins are embedded in this layer
Give 5 roles of membranes
Separating cell components from the outside environment
Separating cell components from cytoplasm
Cell recognition and signalling
Holding the components of some metabolic pathways in place
Regulating the transport of materials into or out of cells
Explain the basic structure of a phospholipid
Phosphate head is hydrophilic (water loving)
Two fatty acid tails are hydrophobic (water hating)
How can a bilayer form?
If phospholipid molecules are completely surrounded by water
If phospholipid molecules are mixed with water, how do they arrange themselves?
They form a layer at the water surface, the phosphate heads stick into the water and the fatty acid tails stick up out of the water
How does a bilayer effectively create a membrane?
The hydrophobic layer formed by the phospholipid tails creates a barrier to many molecules and separates the cell contents from the outside world.
Where do most metabolic reactions take place?
In water-based environments
Through which microscopes can you see membranes?
Electron microscopes
How thick are cell membranes?
7-10nm
What is the protein called that allows water molecules through it?
Aquaporin
What is the name for a model of the biological membrane?
The fluid mosaic model
What are the three main features of the fluid mosaic model?
A bilayer of phospholipid molecules
Various protein molecules floating in the bilayer
Some extrinsic proteins partially embedded in the bilayer and some intrinsic proteins spanning the bilayer completely
What is the difference between a glycoprotein and a glycolipid?
Glycolipids are carbohydrates coming straight from the bilayer
Glycoproteins are carbohydrates coming from a protein embedded in the bilayer
What is the role of cholesterol in the fluid mosaic model?
The provide eukaryotic cells mechanical stability. This is by fitting between the fatty acid tails and helps make the barrier more complete, so water and ions cannot pass easily and directly through the membrane
What do channel proteins do in the fluid mosaic model?
They allow the movement of some substances across the membrane. E.g. Glucose
What do carrier proteins do in the fluid mosaic model?
Actively move some substances across the membrane. E.g. Magnesium ions in plant cells
What do receptor sites do in the fluid mosaic model?
Some allow hormones to bind with the cell so that a response can be carried out. They also let drugs bind which affects cell metabolism
What factor causes cell membranes to become ‘leaky’?
Increasing temperature. This gives cells more kinetic energy so they move faster allowing gaps to be made, making it leaky
In order to detect signals what must cells have on their surface?
‘Sensors’ capable of receiving signals. These sensors are called receptors, they are often protein molecules or modified protein molecules
What is the name of a cell with a receptor for hormone molecules?
A target cell
How is a chemical message passed on to a cell?
The hormone molecule binds to a receptor on a target cell surface membrane because the two have complimentary shapes. This binding causes the target cell to respond in a certain way
What kind of respiration do cells need?
Aerobic
How did the fluid mosaic model get its name?
Fluid mosaic refers to the model of the cell membrane structure. The lipid molecules give fluidity and proteins in the membrane give it a mosaic appearance. The molecules can move about
What is cell signalling?
Cells communicate with one another by signals. Many molecules act as signals - some signal during processes taking place inside the cells others signal from one cell to others. Cytokines are an example of cell signals
What is diffusion?
The movement of molecules from a region of high concentration to a region of lower concentration down a concentration gradient
What is the rate of diffusion affected by?
Temperature Concentration gradient Stirring/moving Surface area Distance/thickness Size of molecule
How does temperature affect diffusion?
Increasing temp gives molecules more kinetic energy, the rate of random movement increases and so the rate of diffusion increases
How does concentration gradient affect diffusion?
Having more molecules on one side of a membrane increases the concentration gradient. This increases the rate of diffusion
How does stirring/moving affect diffusion?
Moving a liquid or creating an air current in a gas increases the movement of molecules and thus the rate of diffusion
How does surface area affect diffusion
Diffusion occurs more rapidly if there is a greater surface area to diffuse across
How does distance or thickness affect diffusion
Diffusion is slowed down by thick membranes, there is a greater distance for the molecule to travel
How does the size of the molecule affect diffusion?
Smaller molecules or ions diffuse more quickly than larger ones
How do lipid based molecules travel across the cell membrane?
They can simply pass through the bilayer, they diffuse down a conc gradient
How do very small molecules and ions travel through the cell membrane?
Carbon dioxide and oxygen molecules are small enough to pass through the bilayer, some water molecules will pass directly through the membrane even though they are polar
How do larger or charged molecules pass through the cell membrane?
Small, charge particles such as sodium ions, or larger molecules such as glucose cannot pass through the lipid bilayer. These molecules are moved via protein channels by facilitated diffusion
What are channel proteins?
They are pores in the membrane which are shaped to only allow one type of ion through, many are also gated meaning they can be open or closed
What are carrier proteins?
These are shaped so that a specific molecule (e.g. Glucose) can fit into them at the membrane surface. When the specific molecule fits, the protein changes shape to allow the molecule through to the other side of the membrane.
What substances are moved through a membrane by simple diffusion?
Gases like oxygen and carbon dioxide
Lipid based molecules like steroid hormones
What substances are moved through a membrane by facilitated diffusion using channel proteins?
Ions like sodium ions and calcium ions
What substances are moved through a membrane by facilitated diffusion using carrier proteins?
Larger molecules like glucose and amino acids
How do protein pumps (using ATP) differ from protein carriers (using facilitated diffusion)?
They carry specific molecules one way across the membrane
Use ATP to carry molecules across
They carry molecules in the opposite direction to the conc gradient
They carry molecules at a much faster rate than by diffusion
What is active transport?
Refers to the movement of molecules or ions across membranes, which uses ATP to drive protein ‘pumps’ within a membrane
Why can carrier proteins only travel molecules one way across the membrane?
The energy used by active transport changes the shape of the carrier protein. This means the specific molecule fits into the protein on one side only.
What processes are used to transport large quantities of material in or out of a cell?
Endocytosis and Exocytosis
What does endocytosis do?
Brings a large amount of material into the cell
What does Exocytosis do?
Moves large amounts of materials out of the cell
How is endo and Exocytosis able to happen?
Membranes can easily fuse, separate and be ‘pinched off’ to form vesicles. This required ATP!
Give some examples of bulk transport
Hormones - the release of insulin into the blood
Plant cells - materials required to build cell wall
White blood cells engulf microorganisms by forming a vesicles around them
What do the different names mean when used to explain bulk transport? Endo Exo Phago Pino
Endo - inwards
Exo - outwards
Phago - solid material
Pino - liquid material
So… The bulk movement of liquid material out of the cell would be described as ‘exopinocytosos’
Name three passive processes
Diffusion
Facilitated diffusion
Osmosis
Name two active processes
Active transport
Endo and Exocytosis
How does diffusion transport molecules?
Down a concentration gradient lipid soluble or very small molecules through lipid bilayer
How does facilitated diffusion transport materials?
Down a conc gradient charged or hydrophilic molecules or ions via channel or carrier proteins
How does osmosis transport materials
Down a water potential gradient through bilayer or protein pores
How does active transport, transport materials?
Against a conc gradient via carrier proteins that use energy from ATP in order to change shape
How do endo and exocytosis transport molecules?
Bulk transport of materials via vesicles that can fuse with or break from the cell surface membrane
What is a solute?
A solid that dissolves in a liquid
What is a solvent
A liquid that dissolves solids
What is a solution
A liquid containing dissolved solids
What is water potential?
A measure of the tendency of water molecules to diffuse from one place to another
Which way does water always move?
From a region of high water potential to a region of low water potential
What happens to the water potential when solutes are dissolved in the water?
As solutes are dissolved, water molecules cluster around them forming a solution. This lowers the concentration of ‘free’ water molecules, and lowers the water potential. The more solute dissolved, the lower the water potential of the solution
What is osmosis
The net movement of water molecules across a partially permeable membrane
Where is the water potential lower:
Pure water
Cells
In cells due to the sugars salts and other substances dissolved in the cytoplasm
What happens in plant cells when they are placed in a solution with a high water potential?
Water molecules move down the water potential gradient INTO the cells by osmosis. The cell will swell causing the cytoplasm and vacuole to push the membrane against the cell wall. The cell is now turgid
What happens to animal cells when they are placed in a solution with a high water potential?
Water will move down the water potential gradient INTO the cells by osmosis, the cells will swell and the membrane will eventually burst open. The cell is now haemolysed
What happens to animal cells when they are placed in a solution with a low water potential?
Water moves out of the cell by osmosis, the cell contents will shrink and the membrane will wrinkle up, the cell is now crenated
What happens to plant cells when they are in a solution with a low water potential?
Water will move out of the cell by osmosis, the cytoplasm and vacuole will shrink. The cell surface membrane will pull away from the cell wall. This is called plasmolysis.
What is water potential measured in and what is the water potential of pure water?
kiloPascals (kPa)
0 kPa
The potential values decrease as more solute is added
How many chromosomes do humans have?
46
In Eukaryotes what is each chromosome wrapped around?
Proteins called histones
What is chromatin
The mix of DNA and histone proteins wrapped together
What is the name of the section where two chromosomes are attached?
The centromere
What is another name for a pair of chromosomes?
A pair of sister chromatids
Before the DNA can be moved, what do the chromatin strands have to do?
Supercoil to form visible chromosomes, each one is sturdy enough to be moved around more easily.
Give a disadvantage of supercoiled DNA
They can’t perform their normal functions in the cell, so the length of time they spend coiled up needs to be as short as possible
What are the stages of the cell cycle?
Interphase - DNA replicates
Mitosis - the nucleus divides and chromatids separate
Cytokinesis - the cytoplasm divides or cleaves
Growth phase - each new cell grows to full size
Give 4 types/reasons for reproduction of cells
Asexual reproduction
Growth
Repair
Replacement
What is mitosis?
The process of nuclear division where two genetically identical nuclei are formed from one parent cell nucleus
What are the stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens during prophase?
Replicated chromosomes supercoil (shorten and thicken)
What happens during metaphase?
Replicated chromosomes line up down the middle of the cell
What happens during anaphase?
The replicas of each chromosome are pulled apart from each other towards opposite poles of the cell
What happens during telophase?
Two new nuclei are formed
What happens during interphase?
Chromosomes replicate, however they are not yet visible
What is the current stage of mitosis when:
Nuclear envelope breaks down and disappears. Centriole divides in two and heads to opposite poles of cell to form the spindle.
Prophase
What stage of mitosis occurs when:
Chromosomes move to the central region of the spindle and each becomes attached to a spindle thread by its cetromere
Metaphase
What stage in mitosis occurs when:
Sister chromatids are separated, each is pulled to the centriole on its own side
Anaphase
What stage in mitosis occurs when:
New nuclear envelope forms around each new chromosome, spindle breaks down and disappears. Chromosomes uncoil so you can no longer see them under the light microscope
Telophase
What part of the cell cycle is happening when:
Whole cell now splits to form two new cells, each one containing a full set of chromosomes identical to its parent
Cytokinesis
What is the name of the only plant cells that can divide by mitosis?
Meristem cells
How does cytokinesis start in animal cells?
On the outside of the cell by ‘nipping in’ the cell membrane
How does cytokinesis start in plant cells?
Starts with the formation of a cell plate where the spindle equator was. New cell membrane and new cell wall material is laid down along this cell plate
What is the definition of a clone?
Genetically identical cells or organisms derived from one parent
How does bacteria divide?
Binary fission
How does mitosis differ from binary fission?
The term mitosis refers only to cell division involving chromosomes.
Bacteria (which uses binary fission) doesn’t have chromosomes it just has one strand of DNA
What are stem cells?
Cells which are potentially capable of becoming any one if the different cell types found in the fully grown organism it came from.
Where are meristem cells located in plants?
At the root and shoot tips and in a ring of tissues in the stem or trunk (which allows for an increase in girth).
What is a genome?
All the genetic material inside an organism (or cell).
What are gametes?
Cells which contain half the adult number of chromosomes
What happens when two gametes (one male and one female) fuse together?
They produce a zygote which then divides by mitosis to grow into a new individual organism
What are diploid cells?
Cells which contain two sets of homologous chromosomes
What are haploid cells?
Only contain one set of chromosomes. Haploid cells are not genetically identical to each other as each pair of homologous chromosomes separates into haploid cells.
Give two ways in which meiosis differs from mitosis
Produces cells containing half the chromosomes
Produces cells which are genetically different from each other and from the parent cell
What is differentiation in terms of cells?
The changes occurring in cells of a multicellular organism so that each different type of cell becomes specialised to perform a specific function
What does the role of a specific cell depend on?
The number of a particular organelle
The shape of the cell
Some on the contents of the cell
What are erythrocytes?
Red blood cells
What are neutrophils?
A type of white blood cell
How are the contents of sperm cells specialised to perform its function?
Many of mitochondria to create energy of movement for the undulipodium (tail)
Head contains specialised lysosomes (called acrosome) that release enzymes to break down outside of egg so nucleus of sperm can fertilise it
How is the shape of sperm specialised to perform its particular function?
Very small
Long and thin to help easing their movement
Single long undulipodium (flagellum) helps propel cell towards egg
How do the contents of the sperm help it to perform its particular function?
Nucleus contains half number of chromosomes of an adult in order to fulfil its role as a gamete
How are root hair cells specialised to perform their particular function?
Cells have a hair-like projection from their surface out into the soil. Greatly increases surface area of root available to absorb water and minerals from the soil
What is the definition of a tissue?
Collection of cells that are similar to each other and perform a certain function. They may be found attached to each other, but not always.
What is the definition of an organ?
Collection of tissues working together to perform a particular function
What is an organ system
An organ system is made up of a number of organs working together to perform an overall life function. E.g. Excretory system or reproductive system
Describe xylem tissue
Xylem tissue consists of xylem vessels with parenchyma cells and fibres. Meristem calls produce small cells that elongate. Their walls become reinforced and waterproofed by lignin. This kills cell contents, end of cells break down so they become continuous long tubes with a wide lumen. It is well suited for transporting water and minerals up the plant, also helps support the plant
Describe phloem tissue
Consists of sieve tubes and companion cells. Meristem tissue produces cells that elongate and line up end to end to form a long tube. Their ends do not break down completely but form sieve plates between cells. Sieve plates allows movement of materials up or down the tubes. Next to each sieve tube is a companion cell, they are metabolically active, their activities play an important role in moving the products of photosynthesis up and down the plant in the sieve tubes
What are the four main categories that animal tissues are grouped into?
Epithelial tissue -layers and lining
Connective tissues - hold structures together and provide support (e.g. Cartilage, bone and blood)
Muscle tissue - cells specialised to contract and move parts of the body
Nervous tissue - cells that can convert stimuli to electrical impulses and conduct those impulses
What are squamous epithelial cells?
Cells that are flattened so they are very thin. Together they form a thin, smooth, flat surface. They are ideal for lining insides of blood vessels
What is ciliated epithelial tissue?
Collection of column shaped cells. Found on inner surface of tubes e.g. Trachea, bronchi and bronchioles
The exposed end of these cells contains cilia. Cilia wave in a synchronised rhythm to move mucus produced by goblet cells
What are the requirements for photosynthesis?
Light
Water supply
CO2 supply
Presence of chlorophyll
Give 5 ways a leaf is adapted to perform its particular function
Transparent upper surface to let light in
Palisade layer of long thin tightly packed cells containing lots of chloroplasts which contain chlorophyll
Loosely packed spongy mesophyll layer for gas circulation
Lower epidermis with pores called stomata each containing two guard cells
Leaf vein system containing xylem and phloem tissues supporting and transporting the leaf contents
How do guard cells work
Contain chloroplasts, cells walls contain spiral thickenings of cellulose. When water is moved into these cells they become turgid and because of the spirals in the walls of the inner edges, only the outer walls stretch. The two guard cells bulge at both ends so a pore opens between them. This pore is known as a stoma (plural stomata)
