1.1 Cell structure Flashcards
What are the two types of cells?
Eukaryotic (plant & animal)
Prokaryotic (bacteria)
What are the differences between eukaryotic and prokaryotic cells?
Prokaryotic cells are much smaller than eukaryotic cells.
Eukaryotic cells contain membrane-bound organelles and a nucleus containing genetic material while prokaryotes do not.
What is the prokaryotic cell wall composed of?
Peptidoglycan
How is genetic information stored in a prokaryotic cell?
It’s 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. They carried genes that provide genetic advantages e.g antibiotic resistance.
What is order of magnitude?
A power to the base 10 used to quantify and compare size
What is a millimetre in metres?
1x10^-3 metres
What is a micrometre in metres?
1x10^-6 metres
What is a nanometre in metres?
1x10^-9 metres
List the components of both plants and animal cells (5)
● Nucleus
● Cytoplasm
● Cell membrane
● Mitochondria
● Ribosomes
List the additional cell components found in plant cells (3)
● Chloroplasts
● Permanent vacuole
● Cell wall
Other than storing genetic information, what is the function of the nucleus?
It controls cellular activities
Describe the structure of the cytoplasm
The fluid component of the cell which contains organelles, enzymes, dissolved ions and nutrients.
What is the function of the cytoplasm?
● The site of cellular reactions e.g. the first stage of respiration
● It’s also a transport medium
What is the function of the cell membrane?
It controls the entry and exit of materials into an out of the cell
What is the function of mitochondria?
The site of later stages of aerobic respiration in which ATP is produced
What is the function of ribosomes?
Joins amino acids in a specific order during translation for the synthesis of proteins
What is the plant cell wall made of?
Cellulose
What is the function of the plant cell wall?
It provides strength and prevents the cell from bursting when water enters by osmosis
What does the permanent vacuole contain?
Cell sap (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 chloroplasts?
The site of photosynthesis
Describe how sperm cells in animals 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.
Describe how nerve cells in animals are adapted to their function
● Long axon allows electrical impulses to be transmitted all over the body from the central nervous system.
● Dendrites from the cell body connect to and receive impulses from other nerve cells, muscles, and glands.
● Myelin sheath insulates the axon and speeds up the transmission of impulses along the nerve cell.
Describe how muscle cells in animals are adapted to their function
● Arrangement of protein filaments allows them to slide over each other to allow muscle contraction.
● Mitochondria to provide energy from muscle contraction.
● Merged cells in skeletal muscle allow muscle fibre contraction in unison.
Describe how root hair cells in plants are adapted to their function
● Large surface area to absorb nutrients and water from surrounding soil.
● Thin walls that do not restrict water absorption.
Describe how xylem cells in plants are adapted to their function
● No upper or lower margins between cells to provide a continuous route for water flow.
● Thick, woody side walls strengthen their structure and prevent collapse.
Describe how phloem cells in plants are adapted to their function
● Sieve plates let dissolved amino acids and sugars be transported up and down the stem.
● Companion cells provide energy needed for active transport of substances along the phloem.
What is cell differentiation?
The process by which cells become specialised
Why is cell differentiation important?
Allows production of different tissues and organs that perform various vital functions in the human body
At what point in their life cycle do most animal cells differentiate?
Early in their life cycle
For how long do plant cells retain the ability to differentiate?
Throughout their entire life cycle
What is the purpose of cell division in mature animals?
Repair and replacement of cells
What changes does a cell go through as it differentiates?
Becomes specialised through acquisition of different subcellular structures to enable a specific function to be performed by the cell
Define magnification
The number of times bigger an image appears compared to the size of the real object
Define resolution
The smallest distance between two objects that can be distinguished
How does a light microscope work?
It 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
● Portable
● Easy to use
● 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 subcellular 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
● Requires training to use
● Only dead specimens can be observed
How can magnification be calculated?
Magnification = Image size / Object size
What is standard form?
A way of expressing numbers - written as a figure between 1 and 10 multiplied by a positive or negative power of 10
Write 0.005 in standard form
5x10^-3
Write 10382 in standard form
1.0382x10^4
How do bacteria multiply? (Triple)
Binary fission (simple cell division)
How often do bacteria multiply? (Triple)
Once every 20 minutes if enough nutrients are available and the temperature is suitable
State two ways in which bacteria can be grown. (Triple)
● Nutrient broth solution
● Colonies on an agar gel plate
What nutrients make up a nutrient broth solution?
All nutrients required for bacteria to grow including nitrogen for protein synthesis, carbohydrates for energy and other minerals
What are uncontaminated cultures of microorganisms needed for? (Triple)
Investigating disinfectant and antibiotic action
Describe the preparation of an uncontaminated culture using aseptic technique
- Use pre-sterilised plastic Petri dishes or sterilise glass Petri dishes and agar gel before using with an autoclave
- Pour the sterile agar gel into the Petri dish and allow time to set
- Sterilise the inoculating loop by passing it through a Bunsen burner flame
- Dip the inoculating loop into the solution of microorganisms and make streaks with the loop on the surface of the agar
- Put the lid on the Petri dish and secure it with tape. Label accordingly then turn and store upside down
- Incubate the culture at 25 degrees celsius in school laboratories
Why must Petri dishes and culture media be sterilised before use?
To kill any bacteria already present
Why must inoculating loops be sterilised by passing them through a Bunsen burner flame?
To kill any bacteria present on the inoculating loop
Why must the Petri dish lid be secured with tape and the whole dish stored upside down?
Stops bacteria in the air contaminating the culture. The lid is not fully sealed to prevent the growth of anaerobic bacteria in a lack of oxygen. It’s stored upside down to prevent condensation from forming and dripping down onto the colonies.
Why are cultures incubated at 25 degrees celsius in school laboratories?
Harmful pathogens are less likely to grow at this temperature
What is the formula used to calculate cross-sectional area of a bacterial colony or clear area around a bacterial colony?
pi x radius squared
How is the number of bacteria in a population after a certain time calculated from the mean division time?
- Calculate the number of times the bacteria will divide in the given time period from the mean division time.
- Use the following equation to calculate the number of bacteria:
Number of bacteria in population at end of time period = number of bacteria at the beginning of the time period x 2^number of divisions in the time period.
Express the answer in standard form if possible
Calculate the number of bacteria that will be present after 3 hours for a population that divides every 15 minutes and has 5 bacterium present now
15 minutes = 0.25 hours
3 /0.25 hours = 12 divisions 5 x 2^12 = 20480 or 2.048 x 10^4
