7 - Cell Structure

Question 1

Microscope

Answer 1

Coarse focus - approximate focusing
Fine focus - precise focusing
Clip - holds slide in place
Stage height adjuster
Light
Diaphragm - adjusts the amount of light reaching the slide
Condenser - focus light (not present in all microscopes)
Stage - supports the slide
Objective lens - magnified the image
Nosepiece - rotates to move desired lens in place
Eyepiece lens - magnifies the image

Eyepiece lens. Objective lens. Total.
X5. X10. X50
X10. X40. X400

Question 2

Protoplasm

Answer 2

All the living parts of the cell

Question 3

Cytoplasm

Answer 3

The living material in a cell outside the nucleus

Question 4

Animal cells as seen using a light microscope

Answer 4

Animal cells are surrounded by an outer membrane called the cell or plasma membrane

this membrane surrounds the protoplasm which is made up of the nucleus and the surrounding cytoplasm

many of the reactions in a cell take place in the cytoplasm

Question 5

Plant cells are seen using a light microscope

Answer 5

Plant cells are enclosed by a rigid cell wall made of cellulose which is a strong structure of carbohydrate
the cell wall give us the strength and makes it less flexible the cell membrane is usually found just inside the cell wall vacuoles contain a fluid called cell sap which is a solution of salt sugar is in pigments plant cells also have a nucleus and cytoplasm
plant cells that are green contain structures called chloroplasts these are structures in which photosynthesis takes place

Question 6

Electron microscopes

Answer 6

Electron microscopes use a beam of electrons instead of light as electrons are visible the images often converted to an image on a TV screen
Electron microscopes can give magnifications of 250,000 and higher this makes electron microscopes ideal for observing very small structures

A transmission electron microscope TEM
sends a beam of electrons through a thin section of the specimen shows internal structure in great detail

A scanning electron microscope SEM
The same as a TEM but surface view Instead of internal

Question 7

Ultrastructure

Answer 7

fine structure, especially within a cell, that can be seen only with the high magnification obtainable with an electron microscope.

Question 8

Ultrastructure of a generalised cell - cell membrane

Answer 8

Membranes are composed of phospholipids and proteins phospholipids have a water loving phosphate group and water heating with Group and are arranged into double layers called by bilayers

The phosphates are on the exposed outer surface with the lipids in the middle in a membrane protein molecules are completely or partially embedded in the phospholipid bilayer

Question 9

Function of membranes

Answer 9

Retain the cell contents
recognise molecules that touch them
control what enters and leaves selectively or semipermeable
Give some support to the cell

Question 10

Nucleus

Answer 10

The nucleus is the control centre of the cell it’s surrounded by a double membrane with numerous nuclear pause which allowed the controlled entry and exit of molecules into and out of the nucleus the nucleus contains strands of DNA

Question 11

Chromosomes

Answer 11

DNA is arranged into structures called chromosomes
every organism has a definite number of chromosomes humans at 46
genes are located randomly along chromosomes
genes inform the cell how to make certain proteins control features such as the number of fingers colour of eyes production of enzymes and thousand more tasks
they are the units of inheritance
when a cell is not dividing chromosomes are very elongated and interwoven in this form they are called chromatin

Question 12

Nuclear pores

Answer 12

allow a type of RNA ribonucleic acid called M RNA a messenger RNA to pass in and out of the nucleus

Question 13

Nucleolus

Answer 13

Makes ribosomes, stains very darkly

Question 14

Cytoplasm

Answer 14

A jelly like liquid that surrounds the nucleus

organelles such as mitochondria chloroplasts and ribosomes are suspended in the cytoplasm

Question 15

Mitochondria

Answer 15

Site of respiration
Mitochondria supply energy to the cell they are surrounded by a double membrane and on the inner membrane especially on the infoldings is where energy is released the more infoldings present the greater surface area for cellular respiration which results in the production of greater quantities of energy eat each mitochondria has its own loop of DNA
cells with many mitochondria such as muscle and liver in animals and meristems in plants produce lots of energy

Cells with a few mitochondria fat in humans and ground tissue and plants produce less energy

Question 16

Chloroplasts plants only

Answer 16

Chloroplasts are green structures in which photosynthesis takes place there surrounded by a double membrane and have membrane stacks which contain the green pigment chlorophyll they also have a loop of DNA

Question 17

Cell wall plants only

Answer 17

The function of the cell wall is to support and strengthen the cell plant cell walls are made of cellulose cell walls are fully permeable

Question 18

Ribosomes

Answer 18

The function of ribosomes is to make protein they are very tiny beadlike structure is made of RNA and protein they work by combining a sequence of amino acid is a form of protein

Question 19

Diagrams

Answer 19

Chapter starts on page 84 diagram for a microscope 7.1
Phospholipid bilayer seven. Six structure of a membrane 7.7 nucleus and Kromozone 7.9 ultrastructure of mitochondria 7.10 ultrastructure of a 7:15. 12 and ultrastructure of an animal cell 7.13 and ultrastructure of a plant cell 7.14
Prokaryotic and eukaryotic cells 7.16

Question 20

Differences between plant and animal cells

Answer 20

Plant cells have a cell wall chloroplasts contain chlorophyll and a large vacuole animal cells do not have these

Question 21

Prokaryotic

Answer 21

Prokaryotic cells do not have a nucleus or a membrane enclosed organelles they are single celled have a circular loop of DNA not surrounded by a membrane do not have a nucleus have small cells do not have a membrane and close structures such as mitochondria and chloroplasts include bacteria

Question 22

Eukaryotic cells

Answer 22

Have a nucleus cell organelles all of which are enclosed by membranes may have membrane enclosed organelles mitochondria and chloroplasts have large cells include animals plants and fungi are more advanced and prokaryotes

Question 23

To be familiar with and use a light microscope

Answer 23

1. 1 lenses are clean
2. 2 lower microscope stage as far as it will go
3. 3 low power objective lens into place
4. 4 microscope slide onto stage
5. 5 clip slide into position
6. 6 the stage from the side and use course adjustment knob is to move
7. 7 for you object if you object
8. 8 adjust course adjustment knob to move the stage down until the object is in focus
9. 9 adjust the amount of light
10. 10 when the object is focused on the low power mode the slide so that the part of the object you wish to view is in the centre of what you can see
11. 11 click the high power objective lens into place
12. 12 the object should be almost a focus if it is not

Question 24

Adjusting light on a microscope

Answer 24

Adjusting the condenser to focus light on the object
adjusting the diaphragm to control the amount of light reaching the object
placing a sheet of paper between the bulb in the microscope causing the light to be diffused

Question 25

To prepare an exam and plant cells using a light microscope

Answer 25

Preparing the slide

1.1 remove outer dry scaly leaves of onion
1.2 use forceps to pull strip of thin transparent epidermis from the inner curve of the leaf
1.3 place a small piece of the epidermal strip on microscope slide
1.4 add a few drops of iodine solution which is a red yellow stain
It stain the nucleus orange and the cytoplasm yellow
1.5 add a coverslip this prevents the cells from drying out and prevents the lens from getting stained lower the coverslip at an angle this eliminates air bubbles
1.6 Remove any excess iodine using a tissue
1.7 the cells can be viewed on standby using a few drops of water instead of iodine solution at the step four

Examined under the microscope

1. 1 the slide can be examined under the microscope in the same way as described in How to be familiar with and use a light microscope
2. 2 the results will appear similar to those shown in diagram 7.18 page 90
3. 3 draw diagrams of what you can see at a lower point and a higher power