CIE A Level Biology (9700) exams from 2022

Revision Notes

1.2.1 Eukaryotic Cell Structures & Functions

Eukaryotic Cell Structures & Functions

Plasma membrane

Cell components_Plasma membrane, AS & A Level Biology revision notesThe structure of the plasma membrane

  

  • This is found on the surface of the cell and behind the cell wall in plant cells and prokaryotic cells
  • Made of a phospholipid bilayer, with proteins and cholesterol
  • Controls the movement of substances in and out of the cell
  • Has receptor proteins to receive information from other cells

 

Cell wall

Cell components_Cell wall, AS & A Level Biology revision notesThe structure of the cell wall

 

  • In plants, this is made of cellulose. In prokaryotic cells peptidoglycan
  • Has narrow threads of cytoplasm called plasmodesmata to connect plant cells
  • Provides support in plants and protection in prokaryotes

 

Nucleus

components_Nucleus, AS & A Level Biology revision notesThe structure of the nucleus

 

  • Contained in a double membrane called the nuclear envelope with many pores
  • Contains chromatin – made of DNA and histones (proteins)
  • Has a smaller structure the nucleolus which produces ribosomes
  • Controls the cell activity by controlling which genes are transcribed 

 

Mitochondria

Cell components_Mitochondria, AS & A Level Biology revision notesThe structure of the mitochondria

 

  • Contained in double-membrane with the inner membrane folded to form cristae
  • The matrix formed by the cristae contains enzymes used for aerobic respiration, producing ATP
  • Has a small circular DNA (mitochondrial DNA) and ribosomes, can produce enzymes and reproduce independently

 

Chloroplast

Cell components_Chloroplast, AS & A Level Biology revision notesThe structure of the chloroplast

 

  • Contained in double-membrane with the inner membrane formed into thylakoids, stacked up to form grana. The grana are joined together by lamellae (thin and flat thylakoid membranes)
  • Contains the photosynthetic pigments such as chlorophyll
  • The site of photosynthesis. Light-dependent stage taking place in the thylakoids and the light-independent stage (Calvin Cycle) taking place in the stroma
  • Has a small circular DNA and ribosomes, can produce enzymes and reproduce independently

 

Ribosome

Cell components_Ribosome, AS & A Level Biology revision notesThe structure of the ribosome

 

  • Floats in the cell cytoplasm or attached to the rough endoplasmic reticulum
  • Made of ribosomal RNA (rRNA) and proteins, has no membrane
  • 80S ribosomes in the cytoplasm
  • 70S ribosomes in prokaryotes, mitochondria and chloroplasts
  • Site of protein synthesis

 

Endoplasmic Reticulum

Cell components_Endoplasmic reticulum, AS & A Level Biology revision notesThe structure of the rough endoplasmic reticulum

 

Rough Endoplasmic Reticulum

  • Surface covered in ribosomes
  • Continuous folds of membrane from the nuclear envelope
  • Processes proteins made by the ribosomes

Smooth Endoplasmic Reticulum

  • Does not have ribosomes on the surface
  • Production, processing and storage of lipids, carbohydrates and steroids

 

Golgi Apparatus (Golgi Complex)

Cell components_Golgi apparatus, AS & A Level Biology revision notesThe structure of the Golgi apparatus

 

  • Flattened sacs of membrane similar to the smooth endoplasmic reticulum
  • Modifies proteins and packages them into vesicles or lysosomes

 

Large Permanent Vacuole

Cell components_Vacuole, AS & A Level Biology revision notesThe structure of the vacuole

 

  • Sac in plant cells surrounded by the tonoplast, selectively permeable membrane
  • Vacuoles in animal cells are not permanent and small

 

Vesicle 

Cell components_Vesicle, AS & A Level Biology revision notesThe structure of the vesicle

 

  • Membrane-bound sac for transport and storage

 

Lysosome 

Cell components_Lysosomes, AS & A Level Biology revision notesThe structure of the lysosome

 

  • Specialist forms of vesicles contain hydrolytic enzymes (enzymes that break substances down)
  • Break down waste materials such as worn-out organelles, used in the immune system and apoptosis (programmed cell death)

 

Centriole

Cell components_Centriole, AS & A Level Biology revision notesThe structure of the centriole

 

  • Hollow fibres made of microtubules, two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division
  • Not found in flowering plants and fungi

 

Microtubules

Cell Components_Microtubule, AS & A Level Biology revision notesThe structure of the microtubule

 

  • Makes up the cytoskeleton of the cell about 25 nm in diameter
  • Made of α and β tubulin combined to form dimers, the dimers are then joined into protofilaments. Thirteen protofilaments in a cylinder make a microtubule
  • The cytoskeleton is used to provide support and movement of the cell

 

Microvilli

Cell components_Microvilli, AS & A Level Biology revision notesThe structure of the microvilli

  

  • Cell membrane projections that increase the surface area for absorption

 

Cilia

Cell components_Cilia, AS & A Level Biology revision notesThe structure of the cilia

  • Hair-like projections made from microtubules
  • Allows the movement of substances over the cell surface

 

Flagella

Cell components_Flagella, AS & A Level Biology revision notesThe structure of the flagella

  • Similar in structure to cilia, made of longer microtubules
  • Contract to provide cell movement for example in sperm cells
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