12.5 studying cells Flashcards
Eukaryotic meaining
means ‘true nucleus’. The DNA of eukaryotes is enclosed by a nuclear membrane. Animal cells are eukaryotic i.e. they have a nucleus. These cells have membrane bound organelles.
examples of eukaryotic cells
Plants, algae, animal, protozoan, and fungi
Strcture and function of nucleus
Structure
-Nuclear envelope/double
membrane and pores
-Chromosomes / Chromatin (DNA associated with histones) —Nucleolus
Function
-Stores genetic information for polypeptide production.
-Site of DNA replication.
-Site of production of mRNA (transcription) and tRNA.
-Site of production of rRNA/ribosomes (Nucleolus)
structure and function of Mitochondrion (singular)
Mitochondria (pleural)
Structure
-Double membrane
-Inner membrane highly folded to form cristae (increase surface area)
-Matrix (liquid part) containing mitochondrial DNA, ribosomes, proteins and lipids.
Function
-Site of ATP production by aerobic respiration.
-Cells that need a lot of ATP have lots of mitochondria. E.g. muscle cells (for muscle contraction) and epithelial cells (for active transport of ions)
Smooth Endoplasmic Reticulum structure + function
Structure
-Highly folded membranes flattened into sacks called cisternae
Function
-Recombines glycerol and fatty acids to make triglycerides. ———Packages triglycerides into vesicles and transports them to the Golgi
Cytoplasmic Ribosome structure and function
Structure
-Made up of 2 subunits that are made of long strands of rRNA AND ribosomal proteins.
-Eukaryotic cell contains 80s cytoplasmic ribosomes.
Function
-Site of protein synthesis from amino acids.
Golgi Apparatus/Body structure and function
Structure
-Flattened sacs made of membrane filled with fluid.
-Golgi vesicles pinch off from the main membrane.
Function
-Sorts, modifies, and packages proteins and triglycerides* into vesicles.
-Golgi vesicles may be used to form lysosomes (see later)..
-Cells with extensive Golgi, packages lots of molecules for export, e.g. enzyme secreting gland cells, or antibodies producing plasma cells.
*Always involves protein.
Lysosome structure and function
Structure
-Membrane-bound organelle that stores and releases (many) hydrolytic enzymes.
Function
-Contain hydrolytic enzymes - Phagocytes are types of white blood cells that contain many lysosomes, as they hydrolyse invading pathogens.
Cell Surface Membrane structure and function
Structure
-Made up of phospholipids, specific transport proteins, and carbohydrates arranged into what is desribed as a fluid mosaic model (covered in later topic).
Function
-Controls the passage of molecules in and out of the cell
Centrioles structure and function
Structure
-Microtubules
Function
-Form a network of spindle fibres onto which chromosomes attach.
Pull chromosomes/chromatids apart during mitosis. These are not found in plant cells
what are features of chloroplast?
Granum
Thylakoid membrane
Stroma
Starch grains
DNA and 70s ribosomes
Granum
Stack of thylakoid membranes
Thylakoid membrane
Contains chlorophyll for photosynthesis & ATP synthase enzyme to produce ATP.
Stroma
Fluid filled part, some of the photosynthetic reactions occur her
Starch grains
The energy storage molecule in plants.
DNA and ribosomes
Contain their own DNA and 70s ribosomes for synthesis of enzymes needed for photosynthesis
What are the structural features of an animal cell?
Microvilli
Mitochondria
Golgi apparatus
Cell membrane
Centromere
80s Ribosomes
Nucleus
Nucleolus
Nuclear membrane
Nuclear pores
Rough endoplasmic reticulum
cytoplasm
lysosomes
Smooth endoplamic reticul
why is the cell wall strong?
many weak hydrogen bonds
what are fungi cell walls made from?
made from chitin not cellulose
Key differences between plant and animal cells
-Cellulose cell wall whereas No cell wall
-Chloroplasts present (not in roots) whereas No chloroplasts
-Large central vacuole whereas No large central vacuole
-Carbohydrates stored as STARCH whereas Carbohydrates stored as GLYCOGEN
- Has no centrioles whereas Has centrioles
prokaryotes
do not have nucleus or other membrane bound organelles.
The DNA of a prokaryotic cell is circular, and it is not associated with histones.
prokaryote vs eukaryote
-DNA is circular and not associated with histones (proteins) whereas DNA is linear (a line) and associated with histones (proteins)
-Contains no membrane bound organelles. (no nucleus, Rough Endoplasmic Reticulum, Smooth Endoplasmic Reticulum, Golgi, Lysosomes) WHEREAS Contains membrane bound organelles I.e., mitochondria, Golgi apparatus, Rough Endoplasmic Reticulum, Smooth Endoplasmic Reticulum, Lysosomes
-Has no ‘true’ nucleus, DNA is free in cytoplasm WHEREAS Has a nucleus, DNA contained within nuclear membrane
- Contains smaller ribosomes (70s) WHEREAS Contains larger ribosomes (80s)
-Some have capsule, one or more flagella, one or more plasmids WHEREAS Do not have capsule
- Has ribosomes for ATP synthesis WHEREAS Does not have ribosomes (has mitochondria)
-Has cell wall made of murein or peptidoglycan WHEREAS Plant cells have a cell wall made of cellulose
Name 2 structures found within a eukaryotic cell that cannot be identified using an optical microscope
Any 2 from
Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane
Name 2 structures found within a eukaryotic cell that cannot be identified using an optical microscope
Any 2 from
Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane
There are 2 types of electron microscope:
- Transmission Electron Microscope (TEM) produces 2 Dimensional (2D images)
- Scanning Electron Microscope (SEM) produces 3 Dimensional (3D images)
Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure. [5] Principles (how it works) Limitations (drawbacks / disadvantages)
Principles:
1. Electrons pass through / enter (very thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;
Limitations:
5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin; 7. Artefacts present;
8. Complex staining method / complex / long preparation time;
Give one advantage of
using a TEM rather than a
SEM.
Higher resolution / higher (maximum) magnification / higher detail (of image); OR Allows internal details / structures within (cells) to be seen / cross section to be taken;
Give one advantage of
using a SEM rather than a
TEM.
Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;
Scientists use optical
microscopes and
transmission electron
microscopes to investigate
cell structure. Explain the
advantages and limitations
of using a TEM to
investigate cell structure.
Advantages:
1. Small objects can be seen;
2. TEM has higher resolution;
3. Wavelength of electrons shorter;
Limitations:
4. Cannot look at living cells;
5. Must be in a vacuum;
6. Must cut section / thin specimen;
7. Preparation may create artefacts (false image);
Describe how you could
make a temporary mount
of a piece of plant tissue to
observe the position of
starch grains in the cells
when using an optical
(light) microscope.
- Add a drop of water to the microscope slide;
- Get a thin section of plant tissue and float on the drop of water;
- Stain with KI solution;
- Lower the cover slip using a mounted needle to avoid air bubbles;
A student viewed impressions of stomata using an optical microscope. She then determined the mean diameter of the stomata. Describe how the student could have used an eyepiece graticule to determine the mean diameter of stomata (3)
- Measure each stomata using an eye piece graticule
- Calibrate the eyepiece graticule against a stage micrometer
- Take at least 5 measurements and calculate a mean (more measurements = more accurate & more representative
A student viewed impressions of stomata using an optical microscope. She then determined the mean diameter of the stomata. Describe how the student could have used an eyepiece graticule to determine the mean diameter of stomata (3)
- Measure each stomata using an eye piece graticule
- Calibrate the eyepiece graticule against a stage micrometer
- Take at least 5 measurements and calculate a mean (more measurements = more accurate & more representative
Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue (3)
- Break open the cells in a blender/ homogeniser and filter to remove cellular debris;
- Place in an ice cold, isotonic, buffered solution;
- Use differential centrifugation; 4. Chloroplasts are in the second pellet;
Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold, buffered isotonic solution. Explain why the solution was:
a) Isotonic b) Ice cold c) buffered
- Prevents osmosis so no osmotic lysis of organelles/named organelle (e.g. mitochondria);
- Reduce/prevent enzyme activity so organelles are not digested;
- Maintain a constant pH so proteins are not denatured;
