Cell Biology - Cell Structure Flashcards
What are the differences between eukaryotic and prokaryotic cells?
Eukaryotic cells are plant and animal cells and contain membrane bound-organelles and a nucleus containing genetic material.
Prokaryotic cells are bacterial cells and are much smaller and contain free floating DNA. They don’t contain mitochondria or chloroplasts.
What is the prokaryotic cell wall composed of ?
Peptidoglycan
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 that are
found free in the cytoplasm separate
from the main DNA - carry genes that provide genetic advantages eg antibiotic resistance
- can be transferred from one cell to another
What are the organelles only found in plants?
Chloroplasts
Permanent vacuole
Cell wall
What is the function of the nucleus?
Controls activities in the cells
Stores genetic information
What is the function of the cytoplasm?
-Liquid substance where chemical reactions occur
-Contains organelles, enzymes and dissolved ions and nutrients
-transport medium
What is the function of the cell membrane?
Controls movement of substances in and out of the cell
What is the function of mitochondria?
Site of aerobic respiration, providing energy
What is the function of ribosomes?
-Where protein synthesis occurs
-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 plant cell wall ?
Provides strength to cell
Prevents the cell from bursting when water enters by osmosis
What is the function of the permanent vacuole ?
Contains cell sap to support the cell, maintaining its turgidity (keeps it rigid)
What is the function of chloroplasts?
Where photosynthesis occurs as it contains chlorophyll which absorbs sunlight
What is cell differentiation?
The process by which cells become specialised to carry out a particular function
Why is cell differentiation important?
Allows production of different tissues and organs that perform vital functions in human body
Describe how sperm cells in animals are adapted to their function
- specialised to carry the male’s DNA to egg cell for successful reproduction
- many mitochondria which supply energy to allow cell to move
-the acrosome (top of head) has digestive enzymes which break down outer layers of membrane of egg cell - streamlined head and long tail to aid swimming
Describe how nerve cells are adapted to their function
- specialised to transmit electrical signals quickly from one place in body to another
- long axon allowing impulses to be carried along long distances and all over the body from cns
-dendrites (extensions from the cell body) means branched connections can form with other nerve cells
-nerve endings have many mitochondria which supply the energy to make special transmitter chemicals (neurotransmitters). These allow impulses to be passed form one cell to another
Describe how muscle cells are adapted to their function
- specialised to contract quickly to move bones causing movement
- lots of mitochondria to provide energy for muscle contraction
-arrangement of protein filaments (myosin and actin) allows them to slide over each other causing muscle to contract - can store a chemical ( glycogen) that is used in respiration by mitochondria
Describe how root hair cells are adapted to their function
- specialised to absorb water by osmosis and mineral ions by active transport from the soil as they are found in the tips and roots
-large surface area to absorb more water and nutrients from soil
-have mitochondria to provide energy from respiration for the active transport of mineral ions
Describe how xylem cells are adapted to the function
-specialised to transport water and mineral ions to the plant from the roots to the shoots
- lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water
-hollow in centre so water can move through
-tubes are joined end to end forming a continuous tube
Describe how phloem cells are adapted to their function
- specialised to transport substances around plant
-sieve plates let dissolved amino acids and sugars be transported up and down stem - pores allow cell sap to flow
- companion cells provide energy needed for active transport of substances along the phloem
At what point 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?
Repost and replacement of cells
What changes does a cell go through as it differentiates?
Becomes specialised through acquisition of different sub-cellular structures to enable a specific function to be preformed by the cell
Define magnification
The number of times bigger an image appears compared to the actual size of the real object
Define resolution
The smallest distance between 2 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 differences between light and electron microscopes
Light: - uses light - low resolution
- easy to use -cheap -live specimens
- focussed by glass lenses -true colour
- low magnification (max x1250) -portable
Electron: -uses electrons -high resolution - need specialist training -expensive -dead specimens - focussed by magnets -black and white/false colour - high mag( max x50,000) - large, can’t be moved
How does an electron microscope work?
It uses a beam of electrons which are focussed using magnets. The elections hit a fluorescent screen which emits visible light, producing an image
Name the 2 types of electron microscopes
Transmission electron microscope
Scanning electron microscope
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?
Allows smaller sub-cellular structures (mitochondria) to be observed in detail
Enables scientists it develop more accurate explanations about how cell structure relates to function
How do bacteria multiply?
Binary fission - cell splits into 2
Explain how to prepare a microscope slide
- place slide on stage
- use lowest x4 objective lens
- adjust light source
- move stage close to objective lens without lens touching slide
- turn focus knob so slide moves away from lens
- use fine focussing knob to get a clear image
- change objective lens so eyepiece lens X objective lens= magnification
- refocus
How often do bacteria multiply?
Once every 20 mins if enough nutrients are available and the temperature is suitable
State 2 ways bacteria can be grown
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?
Investigating disinfectant and antibiotic action
Why can’t viruses be grown on agar?
Because they need living cells to reproduce
They have to be grown inside suitable host cells
Describe the preparation of an uncontaminated culture using aseptic technique
- use pre-sterilised plastic patio dishes or sterilise glass petri dishes and agar gel before use to kill unwanted microorganisms
- pour the sterile agar gel into 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 surface of the agar - put the lid on the petri dish and secure it with tape. Label and then turn and store it upside down
- incubate the culture at 25 degrees in school laboratories
Why must Petri dishes and culture media (agar) be sterilised before use?
To kill any bacteria already present
Why must inoculating loop be sterilised by passing it through Bunsen burner flame?
To Kill any bacteria present on the inoculating loop
Why must Petri dish lid be secured with tape and the whole dish stored upside down?
-Stops bacteria in air contaminating the culture
-The lid is not fully sealed to prevent the growth of anaerobic bacteria in a lack of oxygen
-stored upside down to prevent condensation from forming and dripping down onto the agar/colonies
Why are cultures incubated at 25 degrees in school lavatories?
Harmful pathogens are less likely to grow at this temperature
What is the formula to calculate the area of a bacterial colony?
Pi 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 mean division time
- use equation: number of bacteria in population at end of time period= number of bacteria at beginning of time period X 2 to the power of numbers of divisions in time period
Calculate conversions
nm —/1000–micrometers—/1000–mm—/1000–m
