CIE AS Biology notes

CELL STRUCTURE
1.1 M I C R O S C O P Y

• Enables us to examine organisms and structures
• MAGNIFICATION : number of times larger an image is compared to the real
size of an object
- OBSERVED SIZE OF IMAGE : what you can measure using a ruler
- ACTUAL SIZE : real size / before magni ed
• RESOLUTION : ability to distinguish between 2 objects very close
together
- The higher the resolution, the greater the detail

• Types of microscopes :
- Light microscope -> uses light - Electron microscope -
electrons
- If object is smaller than half the
wavelength, it can’t be seen - Samples must be p
separately from nearby objects vacuum and prepa
water boils = use d
- 400 nm = violet to 700 nm =
- Opposite advantag
red
disadvantages of l
- Cheap - Lower magni cation - Types :
- Portable - Lower resolution - TRANSMISSION E
- Can use live MICROSCOPE( TE
organisms beam passed th
specimen befor
- SCANNING ELECT
( SEM ) : electr
surfaces of stru
re ection beam
- Can see surf
- Can see in 3
LIGHT ELECTRON
- Lower resol
Resolution 0.2 µm 0.5 nm 1. Metal heats -> elec

,• Electron micrograph :
- Darker in certain areas = denser = absorbs more electrons
- ULTRASTRUCTURE : the detailed structure of a cell revealed by the electr

• Measuring cell size :
- STAGE MICROMETER : very small and accurately drawn scale of known di
- EYEPIECE GRATICULE : small scale that is placed in a microscope eyepiece
Graticule Unit ( EGU )
1. Find out actual size -> how many EPU go into stage micrometer scale
- The whole eyepiece graticule scale into stage micrometer scale
2. Convert measurements if necessary
3. Find out length / width of organism using eyepiece graticule scale
4. Length / Width x Actual size
1. 100 EGU
2. 0.25 mm
3. Cheek ce
4. 20 x 2.5




- Using scale bar :
1. Length of organism
1. Measure scale bar
2. 36 mm = 36 000 µm
2. Convert if necessary -> I
3. Use equation 3. M = I / A
- Scale bar is A = 36

= X60




• Conversions : PREFIX NU

, 1.2 CELL S AS BASIC UNITS OF LIVIN G ORG

• In animal and plant cells :
- NUCLEUS ( 10 µm ) : dense, contains - CYTOPLASM : aqueous m
genetic material / DNA -> protected like consistency -> co
DM from degradation by enzymes - PROTOPLASM : all li
- NUCLEAR ENVELOPE : surrounds inside a cell
nucleus
- MICROTUBULES ( 25
- NUCLEAR PORE : gaps in nuclear rigid, hollow tubes
envelope -> exchanges between protein, makes up
nucleus and cytoplasm determines cells sh
- Substances leaving : mRNA intravenously tran
and ribosomes holds membrane b
- Substances entering : protein, in place
nucleotide, ATP and hormones - Made of α - tub
- CHROMATIN : loosely coiled threads and β - tubulin
-> forms CHROMOSOMES in nuclear form dimers ->
division to form proto
( polymerisatio
- Consists of DNA and proteins
- 13 proto la
- NUCLEOLUS : loops of DNA alongside ea
from several chromosomes cylinder for
- Manufactures ribosomes - CENTROSOMES ( not
using info from own centrioles ( 18 mic
DNA right angles -> ass
microtubules and f
bres, microtubule
centre

- CELL SURFACE MEMBRANE / PLASMA - RIBOSOMES ( 25 nm ) :
MEMBRANE ( 7 nm ) : thin, surrounds synthesis, made of RN
the cell, selectively permeable acid ) and protein
membrane, exchanges biological - S UNITS : measure
molecules and ions, cell recognition, substances sedime
cell - to - cell adhesion, forms speed centrifuge
hydrogen bonds for water - The faster the s
- PHOSPHOLIPID BILAYERS : makes cell higher the S nu

, - ENDOPLASMIC RETICULUM : network of - MITOCHONDRIA ( 1 µ
SM
attened sacs out aerobic respira
- Packages synthesised into - INNER MEMBRAN
vesicles and transport to golgi barrier controll
- ROUGH ENDOPLASMIC RETICULUM : ions and molec
covered in ribosomes -> large SA - Matrix con
for protein synthesis respiration
- Bumpy due to ribosomes ribosomes a
DNA
- SMOOTH ENDOPLASMIC RETICULUM : - CRISTAE : foldin
tubular membrane vesicles with
membrane -> p
uid - lled sacs, makes lipids
interior solutio
and steroids, storage site for
calcium ions -> more in muscle - PORIN : transpo
cells outer membran
wide aqueous
- Smooth due to less ribosomes channel ->
allows molecul
from cytoplasm
intermembrane
space

- GOLGI BODY / COMPLEX / APPARATUS : uid - LYSOSOMES ( 0.1 - 0.5
- lled and attened sacs, modi es sacs, no internal struc
proteins and lipids synthesised in RER down unwanted struc
SM and SER, transports / modi es / stores worn out organelles, c
lipids digestive enzymes tha
- GOLGI VESICLES : carries the separate from rest of
packages, makes lysosomes damage, exocytosis
- In WBC, used to dige

- CILIA and FLAGELLA : whip like structures, projects from cell surface -> b
movement of uid across cell surface
- Same but agella is longer