aqa gcse combined science b1

cell biology

what is a cell?

the basic unit of living organisms

where are eukaryotic cells found?

* plants
* animals
* fungi
* protists

what is the size of eukaryotic cells?

10-100 micrometres

what is the size of prokaryotic cells?

0\.1-5.0 micrometres in size

what are the differences between prokaryotic and eukaryotic cells?

* prokaryotic cells have no nucleus
* prokaryotic cells have no mitochondria or chloroplasts
* prokaryotic cells have plasmids

what sub-cellular structures do animal cells contain?

* cell membrane
* nucleus
* ribosomes
* mitochondria
* cytoplasm

what sub-ceullar structures do plants have that animal cells don’t?

* permanent vacuole
* chloroplasts
* cell wall

when can plant cells differentiate?

throughout their lives

when can animal cells differentiate?

early in their development

what are the sub-cellular structures inside of a prokaryotic cell?

* cell wall
* cell membrane
* cytoplasm
* flagella
* plasmids

what is cell differentiation?

the process where a cell develops new sub-cellular structures to let it perform a specific function

what are sperm cells specialised to do?

fertilise egg cells

what are the adaptations of sperm cells?

* tail - fast travel
* head - contains nucleus
* acrosome - contains enzyme to penetrate egg cell
* middle section - mitochondria filled to provide energy

how is a nerve cell specialised to transmit electrical messages around the body?

* axon - long to increase the distance that electrical signals can travel
* myelin sheath - stops signals leaking
* dendrites - spread outwards to transfer electrical messages to other neurons

how are muscle cells specialised?

* many mitochondria - energy for motion
* protein fibres - can contract for motion

how are root hair cells specialised?

* no chloroplasts - no photosynthesis
* long projections - increase sa:v ratio

how is the xylem cell specialised to transport water up the stem of a plant and into the leaves?

* open ended cells - water can move through
* lignin - strengthen walls

how is phloem specialised to transport food products to part of the plant?

* small holes - allow food products to move

what is magnification?

how many times larger an image seen through a microscope is compared to the real object

what is resolution?

the ability to distinguish between two or more objects that are close together

when was the first light microscope created?

late 16th century

what discoveries have been made by light microscopes?

* bacteria to be seen for the first time
* see plant and animal cells separately

when was the first time the electron microscope was used?

1933

what discoveries were made with electron microscopes?

* sub-cellular structures
* study mitochondria, ribosomes and chloroplasts

what are chromosomes?

made of molecules of DNA and are found in the nucleus of cells

what is the cell cycle?

* initial growth stage where extra ribosomes, mitochondria and other SCS are produced
* cells chromosomes are replicated
* mitosis where the sets of chromosomes are pulled away and nucleus is divided
* cell divides into two identical cells

what are stem cells?

undifferentiated cells that have not yet specialised to perform a specific function

where are stem cells found?

* embryos
* plant meristems
* bone marrow

what are the uses of stem cells?

* stem cell treatments - to replace damaged cells
* plant clones - quick and cheap clones
* therapeutic cloning

what are the disadvantages of stem cells?

* could transfer viral infections
* ethical beliefs

what are the factors affecting diffusion?

* increased temp = faster diffusion rate
* bigger concentration gradient = faster diffusion= rate
* large membrane surface area = faster

what is the concentration gradient?

the difference in concentration between two areas

what adaptations do exchange surfaces have?

* large surface area
* thin membrane
* ventilation
* blood supply

what are exchange surfaces?

surfaces adapted to maximise the efficiency of gas and solute exchange across them

what are examples of exchange surfaces?

* small intestine
* lungs
* gills
* roots
* leaves

what is osmosis?

a special case of diffusion where water moves across a partially permeable membrane from a dilute solution to a concentrated solution

what is a partially permeable membrane?

a membrane that allows water through but won’t let larger molecules dissolved in water through

where is active transport used?

* in the human gut to absorb sugar molecules for respiration
* mineral absorption in plants and roots

what is active transport?

the net movement of particles against a concentration gradient