Biology AQA-1.Cell Biology

eukaryotic cells have a 3 things enclosed in a nucleus

cell membrane, cytoplasm and genetic material

prokaryotic cells 3 facts

-smaller in size

-genetic material is not in a nucleus

-has a dna loop and small rings of dna called plasmids

order of magnitude

centi,milli,micro,nano

nucleus

controls the celland contains genetic material.

cytoplasm

where chemical reactions happen

cell membrane

controls the movement of substances in and out of the cell

mitochondria

generates energy through respiration

ribosomes

synthesize proteins

chloroplasts

plant cells, where photosynthesis happens

permanent vacuole

plant cell, stores cell sap

Cells may be specialised to carry out a particular function:

sperm cells

specialised for reproduction

-tail for swimming

-lots of mitochondria for energy

Cells may be specialised to carry out a particular function:

nerve cells

specialised for rapid signalling

-long to cover distances

-branched connections to connect to each other

Cells may be specialised to carry out a particular function:

muscle cells

specialised for contraction

-long for space to contract

-lots of mitochondria for energy

Cells may be specialised to carry out a particular function:

root hair cells

specialised for absorbing water and minerals

-long hairs for a larger surface area

-no chloroplast as they are underground

Cells may be specialised to carry out a particular function:

xylem

specialised for transporting food from the leaves to the rest of the plant

-small pores in end walls to allow sap to flow through

-translocation(transportation goes in both directions)

Cells may be specialised to carry out a particular function:

phloem

specialised for carrying water and mineral ions up the plant

-dead cells joined with no end walls

-strengthened with lignin

Many types of plant cells retain the ability to…

differentiate

Most types of animal cell differentiate at…

an early stage

purpose of cell division

growth and repair

light microscopes

use light and lenses to form an image and magnify it

electron microscopes

higher magnification and resolution

Bacteria multiply by…

binary fission

explain why:

Petri dishes and culture media must be sterilised before use and inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame

to kill unwanted microorganisms

explain why:

lid of the Petri dish should be secured with adhesive tape

to stop microorganisms from the air getting in, but not fully as they need some oxygen

explain why:

lid of the Petri dish should be stored upside down

to stop drops of condensation falling on the agar

explain why:

school and college laboratories, cultures should be incubated at a maximum temperature of 25°C

minimize the growth of harmful pathogens that thrive at human body temperature

nucleus of a cell contains…

chromosomes made of DNA molecules

Each chromosome carries a large number of…

genes

chromosomes are normally found in…

pairs

describe the stages of the cell cycle, mitosis.

1.genetic material is doubled and then divided into two identical cells

2.increase the number of sub-cellular structures such as ribosomes and mitochondria

3.DNA replicates to form two copies of each chromosome

4.In mitosis one set of chromosomes is pulled to each end of the cell and the nucleus divides

5.the cytoplasm and cell membranes divide to form two identical cells

A stem cell is an…

undifferentiated cell

describe the function of stem cells in:

embryos

human embryos can be cloned and made to differentiate into most types of human cells

describe the function of stem cells in:

adult bone marrow

can form many types of cells including blood cells

describe the function of stem cells in:

meristems in plants

can differentiate into any type of plant cell

Treatment with stem cells may be able to help conditions such as…

diabetes and paralysis.

Stem cells from meristems in plants can be used to produce clones of plants quickly and economically:

• Rare species can be cloned to protect from extinction.

• Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

Diffusion

movement from an area of higher concentration to an area of lower concentration

such as oxygen and carbon dioxide in gas exchange

Factors which affect the rate of diffusion:

difference in concentrations (concentration gradient)

the greater the concentration difference, the faster the movement will occur

Factors which affect the rate of diffusion:

temperature

Higher temperatures means faster diffusion rates as particles have more kinetic energy, causing them to move and mix more quickly

Factors which affect the rate of diffusion:

surface area of the membrane

A larger surface area allows for more molecules to pass through the membrane ,increasing the rate of diffusion

explain how the small intestine are adapted for exchanging materials

-a large surface area with villi and microvilli

-a short diffusion distance, villi are only one cell thick

-a good blood supply, maintaining a concentration gradient

explain how the lungs are adapted for exchanging materials

-a large surface area with alveoli

-a short diffusion distance, walls of the alveoli and the capillaries surrounding them are very thin

-a good blood supply, maintaining a concentration gradient

explain how the gills in fish are adapted for exchanging materials

-large surface area of the gills

-the large surface area of the blood capillaries in each gill filament

-the short distance required for diffusion – the outer layer of the gill filaments and the capillary walls are just one cell thick

explain how the roots in plants are adapted for exchanging materials

-large surface area as root network is highly branched and has root hair cells

explain how the leaves in plants are adapted for exchanging materials

-stomata to decrease the diffusion distance

-lower layer is made from spongy mesophyll to allow air to circulate

Osmosis

diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane

Active transport

substances from a more dilute solution to a more concentrated solution (against a concentration gradient)

Active transport requires…

energy from respiration