cells and microscopy

animal cells

cell organelles:

• nucleus - contains genetic material (DNA) which controls the activities of the cell

• cytoplasm - where most chemical reactions happen

• mitochondria - respiration happens in the mitochondria that provides energy for the cell

• cell membrane - creates barrier for the cell, controls what can flow in and out of the cell

• ribosomes - found in the cytoplasm and make proteins. They ‘read’ dna and build proteins from that.

it is a eukaryote

plant cell

they contain everything the animal cell card listed and more

cell organelles:

• chloroplast - absorb light energy for photosynthesis. Only found in some plant cells

• vacuole - filled with cell sap, keeps it turgid and suppourts the structure of the plant

• cell wall - made of celllose, strengthens the plant cell, helps maintain shape

it is a eukaryote

prokaryotes (bacteria)

they have no nucleus or mitochondria

prokaryote organelles:

• cell membrane

• cell wall

• slime capsule - protects bacteria but not in every bacteria

• loop of genetic material

• plasmid - small circular dna

• flagellum - allows movement only in some bacteria

• ribosomes

prokaryotes and eukaryotes

cells can either be prokaryotic or eukaryotic.

eukaryotic cells are complex and include all animal and plant cells. Prokaryotic cells are smaller and simpler e.g. bacteria

eukaryotes are organisms made up of eukaryotic cells

a prokaryote is a prokaryotic cell (its a single celled organism)

both eukaryotic and prokaryotic cells contain various cell parts called subcellular structures

exam question - compare a prokaryote and a eukaryote

Model Answer

• Similarities: Both cell types possess a cell membrane, cytoplasm, ribosomes (for protein synthesis), and genetic material (DNA).

• Differences - Genetic Material: Eukaryotic cells contain their DNA within a membrane-bound nucleus, whereas prokaryotic DNA is found free-floating in the cytoplasm in a region called the nucleoid. Additionally, prokaryotes often have small, circular DNA rings called plasmids, which are rarely found in eukaryotes.

• Differences - Organelles: Eukaryotes contain membrane-bound organelles such as mitochondria and chloroplasts, which are absent in prokaryotic cells.

prepare a slide - human cheek cell

1. use a cotton bud to swab some cells off the inside of your cheek

2. smear it on a slide and put a couple drops of methylene blue

3. place a cover onto the methylene and place under microscope

required practical - preparing a slide to view onion cells

1. add a drop of water to clean the slide

2. cut up some onion and separate it out in layers. Use twezers to peel off some epidermal tissue from the bottom of one of the layers

3. using tweezers, place the epidermal tissue into the water on the slide

4. add a drop of iodine solution to stain/ highlight objects in a cell by adding colour to them

5. place a cover slip, tilt and lower so no air bubbles that might obstruct view of specimin

required practical - observing the onion cell specimin

1. clip the slide onto the stage

2. select lowest powered objective lens (lowest magnification)

3. use coarse adjustment knob to move stage up and down to just below objective lens

4. look down eye piece. turn knob until in focus

5. adjust the focus with the fine adjustment knob until the image is roughly in focus

6. adjust more until you get a clear image of whats on the slide

7. if you need to see the slide with a greater magnification, swap to a higher powered objective lens and refocus.

required practical - drawing observations of onion cell

when drawing your specimin use a sharp pencil to draw clear unbroken lines, no colouring or shading, if you are drawing cells the subcellular structures should be drawn in proportion and if you are asked to draw a certain drawing it has to take up at least half of the space available. Also when labelling, use straight uncrossed lines and work out the magnification of the drawing.

specialsed cells defenition

a specialized cell is a cell that performs a specific function. Most cells in an organism are specialised

why do animals have specialised cells

Animals have specialized cells to efficiently perform specific, complex tasks necessary for survival, such as movement, oxygen transport, and nutrient digestion.

compare a specialsed and a generalised cell

• Shape: Generalized cells are often depicted as simple, rounded, or irregular. Specialized cells have specific, often complex shapes (e.g., long, thin axons for nerve cells, biconcave shapes for red blood cells) to facilitate their function.

• Organelle Abundance: Specialized cells alter organelle numbers to fit their role. For example, muscle cells contain high numbers of mitochondria for energy, while sperm cells have an acrosome for enzyme storage.

• Unique Features: Specialized cells may possess unique structures, such as the contractile, striated fibers in muscle cells or the flagellum tail on a sperm cell.

• Nucleus Presence: Some specialized cells, such as mature red blood cells in humans, lack a nucleus to maximize space for carrying oxygen, unlike a generalized cell which contains a nucleus.

muscle cells

musclec cells are specalized for contraction. The function of a muscle cell is to contract quickly. These cells so long (so they have space to contract) and contain lots of mitochondria to transfer the energy needed for contraction.

specialized cell - nerve cell

function - recives and sends messages from the body and back to the brain

adaptation - covered in fat to prevent electrical impulses

specialized cell - sperm cell

function - to carry the fathers genetic info (dna) when fertilizing the egg

adaptation - have long tail to swim fast to find the egg, lots of mitochondria in the cell to provide energy it needs to do this. It also carrys enzymes in its head to digest through the egg cell membrane

specialized cell - ciliated cell

function - stop lung damage and sweeps mucus and trapped dust and bacteria to be swallowed

adaptation - they line the air passages down to the lungs

specialized cell - egg cell

function - carrys the mothers dna and suppourts a growing embryo

adaptation - contains half the dna required to make a person

specialized cell - red blood cell

function - carrys oxygen from lungs to body

adaptation - large surface area with concave shape, has no nucleus to make room for more oxygen

specialized cell - palisade cell

function - to carry out photosynthesis

adaptation - packed with chloroplasts to absorb sunlight

specialized cell - root hair cell

function - absorbs minerals and water from soil

adaptation - large surface area to absorb lots of water

a scientific drawing of a root hair cell observed using a light microscope

specialized cells - phloem and xylem

function - they are specialised for transporting substances. They form phloem and xylem tubes which transport water and food around plants. To form the tubes, the cells are long and joined end to end. Xylem cells are hollow in the centre and phloem cells have very few subcellular structures

adaptation - Xylem and phloem are vascular tissues with specialized adaptations for transport. Xylem (dead cells, lignin, no end walls) efficiently moves water upward via transpiration. Phloem (living cells, sieve plates, companion cells) facilitates bi-directional translocation of sucrose and amino acids. Both form organized bundles to provide structural support.

cell differentiation

differentiation is the process by which a cell changes to become specialised for its job. As cells change, they develop different sub-celullar structures and turn into different types of cells

most differentiation occurs as an organism develops. In most animal cells, the ability to differentiate is then lost after they become specialised however lots of plant cells dont lose this ablility. The cells that differentiate in mature animals are mainly used for repairing and replacing skin cells and blood cells

some cells are undifferentiated and they are called stem cells

resolution

the smallest distance you can see between two seperate points

light microscope

magnification - 300-2000 x larger

resolution - cant resolve distance smaller than 200nm (half of a visible light wave)

electron microscope

magnification - 2,000,000 x larger

resolution - as small as 0.2nm but 3d can only do 10nm

have to be kept in rooms with controlled temp, pressure and humidity

microscopesy conversions

cm →mm = x10

cm →um = x10,000

mm →um = x1000

um →nm = x1000

mm →cm = /10

um →cm = /10,000

um →mm = /1000

nm →um = /1000

parts of a microscope

magnification equation

magnification = image size / real size