Flashcards - Topic 1 Cells and microscopy - Edexcel Biology GCSE
State the two types of cell
Eukaryotic (animals and plants) and prokaryotic
What is the difference between a eukaryotic and a prokaryotic cell?
A eukaryotic cell contains a nucleus and membrane-bound organelles. A prokaryotic cell does not.
List the components of both plant and animal cells (5)
- Nucleus
- Cytoplasm
- Cell membrane
- Mitochondria
- Ribosomes
How is genetic information stored in a eukaryotic cell?
Within the nucleus, arranged in chromosomes
Other than storing genetic information, what is the function of the nucleus?
Controls cellular activities
Describe the structure of the cytoplasm
Fluid component of the cell containing organelles, enzymes, and dissolved ions and nutrients
What is the function of the cytoplasm?
Site of cellular reactions e.g. first stage of respiration
What is the function of the cell membrane?
Controls the entry and exit of materials into and out of the cell
What is the function of the mitochondria?
Site of later stages of aerobic respiration in which ATP is produced
What is the function of the ribosomes?
Joins amino acids in a specific order during translation
Which organelles are found in plant cells only? (3)
- Large, permanent vacuole
- Cell wall
- Chloroplasts
What is the cell wall made of?
Cellulose
What is the function of the cell wall?
Provides strength and prevents the cell bursting when water enters by osmosis
What does the permanent vacuole contain?
A solution of salts, sugars, and organic acids
What is the function of the permanent vacuole?
Supports the cell, maintaining its turgidity
What is the function of the chloroplasts?
Site of photosynthesis
When looking at a cell using a light microscope, why do chloroplasts appear green?
Contain chlorophyll, a green pigment
List the organelles found in prokaryotic cells (6)
- Chromosomal DNA
- Plasmid DNA
- Cell wall
- Cell membrane
- Ribosomes
- Flagella
How is genetic information stored in a prokaryotic cell?
Found free within the cytoplasm as: Chromosomal DNA (single large loop of circular DNA) and Plasmid DNA
What are plasmids?
Small, circular loops of DNA found free in the cytoplasm and separate from the main DNA. Carry genes that provide genetic advantages e.g. antibiotic resistance
What is the prokaryotic cell wall composed of?
Peptidoglycan
What is a flagellum?
Long, rotating, ‘whip-like’ protrusion that enables bacteria to move
What is a haploid cell?
A cell that contains a single copy of each chromosome (half the number of chromosomes) e.g. 23 chromosomes in humans
What is a diploid cell?
A cell that contains two copies of each chromosome (full set of chromosomes) e.g. 46 chromosomes in humans
What are gametes?
Reproductive cells (e.g. egg and sperm cells) that are haploid cells
Describe sexual reproduction in terms of chromosome number
Two haploid gametes fuse, resulting in an embryo with two chromosomes for each gene and two copies of each allele ∴ diploid
Describe how egg cells are adapted to their function
- Haploid nucleus contains genetic material
- Mitochondria in cytoplasm produce energy for the developing embryo
- Cytoplasm contains nutrients for the developing embryo
- Cell membrane hardens after fertilisation, preventing the entry of other sperm and ensuring the zygote is diploid
Describe how sperm cells are adapted to their function
- Haploid nucleus contains genetic information
- Tail enables movement
- Mitochondria provide energy for tail movement
- Acrosome contains enzymes that digest the egg cell membrane
Where are ciliated epithelial cells found?
Found lining the surface of structures such as the respiratory tract and uterus
Describe the function of ciliated epithelial cells lining the airways
Move in synchronised waves to beat mucus (containing dirt and pathogens) up to the back of the throat where it can be swallowed
What is magnification?
The number of times bigger an image appears compared to the size of the specimen
How can the total magnification of an image be calculated from lens powers?
How can the magnification of an image be calculated?
What is resolution?
The smallest distance between two objects that can be distinguished
How does a light microscope work?
Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed
What are the advantages of light microscopes? (4)
- Inexpensive
- Easy to use
- Portable
- Observe both dead and living specimens
What is the disadvantage of light microscopes?
Limited resolution
How does an electron microscope work?
It uses a beam of electrons which are focused using magnets. The electrons hit a fluorescent screen which emits visible light, producing an image.
Name the two types of electron microscope
- Transmission electron microscope (TEM)
- Scanning electron microscope (SEM)
What is the advantage of electron microscopes?
Greater magnification and resolution
Why do electron microscopes have a greater magnification and resolution?
They use a beam of electrons which has a shorter wavelength than photons of light
How have electron microscopes enabled scientists to develop their understanding of cells?
- Allow small sub-cellular structures (e.g. mitochondria, ribosomes) to be observed in detail
- Enable scientists to develop more accurate explanations about how cell structure relates to function
What are the disadvantages of electron microscopes? (4)
- Expensive
- Large so less portable
- Require training to use
- Only dead specimens can be observed
How do you convert from m to mm?
× 1000 (× 10^3)
How do you convert from m to µm?
× 1 000 000 (× 10^6)
How do you convert from m to nm?
× 1 000 000 000 (× 10^9)
How do you convert from nm to m?
÷ 1 000 000 000 (× 10^-9)
How do you convert from m to pm?
× 1 000 000 000 000 (× 10^12)
Write 0.005 in standard form (higher)
Write 10382 in standard form (higher)
Convert 1.527 m to µm. Write your answer in standard form (higher)
1.527 m × 1000000 = 1527000 µm
What is simple diffusion?
The net movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient
What molecules enter and leave cells via simple diffusion through the cell membrane?
Small molecules e.g. oxygen, water, glucose, amino acids
What factors affect the rate of diffusion? (3)
- Temperature
- Concentration gradient
- Surface area of cell membrane
Define osmosis
The net movement of water molecules from an area of high water concentration to an area of low water concentration through a partially permeable membrane
What is active transport?
The movement of molecules across a cell membrane from an area of low concentration to an area of high concentration, against the concentration gradient, using energy
How is a percentage change in mass calculated?
Percentage change in mass = (final mass - initial mass) / initial mass x 100%
What are enzymes?
Biological catalysts that increase the rate of a chemical reaction without being permanently altered themselves.
What is an advantage of enzymes in the body?
They enable cellular reactions to take place at lower temperatures.
What is the active site of an enzyme?
The region of an enzyme to which a substrate molecule binds and the reaction takes place.
Why are enzymes described as having a ‘high specificity’ for their substrate?
Only substrates with a specific, complementary shape can fit into an enzyme’s active site.
Describe the ‘lock and key’ model.
Substrate collides with the active site of an enzyme, substrate binds, enzyme-substrate complex forms, substrate converted to products, products released from the active site which is now free to bind to another substrate.
What factors affect the rate of an enzyme-controlled reaction?
- Temperature
- pH
- Substrate concentration
Explain how increasing temperature initially affects the rate of an enzyme-controlled reaction.
As temperature increases, molecules have more KE, movement of molecules increases, probability of a successful collision increases, more enzyme-substrate complexes form, rate of reaction increases.
Explain how increasing temperature above the optimum affects the rate of an enzyme-controlled reaction.
Temperature increases above the optimum, increased vibrations break bonds in enzyme’s structure, active site changes shape, enzyme is denatured, no more enzyme-substrate complexes can form, rate of reaction decreases.
Explain how pH affects the rate of an enzyme-controlled reaction.
Enzymes have an optimum pH, pH shifts from the optimum, bonds in the enzyme’s structure are altered, active site changes shape, enzyme is denatured, rate of reaction decreases.
Explain how the substrate concentration affects the rate of an enzyme-controlled reaction.
Substrate concentration increases, number of substrate molecules in the same volume increases, probability of a successful collision increases, more enzyme-substrate complexes form, rate of reaction increases, once all active sites become full, the rate of reaction plateaus.
What are the units for rate?
s-1
Why must large organic molecules be broken down into smaller, simpler molecules in the body?
Large molecules are too big to be absorbed across the surface of the gut wall.
Give an example of the breakdown of large molecules into smaller molecules in plants.
Starch is broken down by enzymes into simpler sugars which are respired to release energy.
What type of molecules are proteins and carbohydrates?
Polymers.
What are the monomers of carbohydrates?
Simple sugars.
Which group of enzymes catalyses the breakdown of carbohydrates?
Carbohydrases.
Which type of carbohydrase catalyses the breakdown of starch?
Amylase.
What are the monomers of proteins?
Amino acids.
Which type of enzyme catalyses the breakdown of proteins?
Proteases.
What is the function of lipases?
Enzymes which catalyse the breakdown of lipids into fatty acids and glycerol.
Why are small molecules synthesised into larger organic molecules in the body?
Large molecules are used for storage (e.g. glycogen) or are used to build structures (e.g. organelles).
Which enzyme catalyses the formation of glycogen from glucose?
Glycogen synthase.
How can the amount of energy contained in food be measured?
Measured using calorimetry.
What is calorimetry?
A method of measuring the heat transfer during a chemical reaction.
Describe the method used to measure the amount of energy in a sample of food.
Add a set volume of water to a boiling tube, record initial temperature, record the mass of a small sample of food (e.g. bean), stick the sample onto a mounted needle, using a bunsen burner light the food sample, hold the sample under the boiling tube until it burns up, record the maximum temperature reached by the water, record the final mass of the food sample.
