HOW THE STRUCTURE OF CELLS IS RELATED TO THEIR FUNCTION
INTRODUCTION- Mention diversity of cells in plants and animals with examples. Cells have adapted for a
wide range of specific functions through evolution.
ANIMALS
STANDARD ANIMAL CELL
Golgi apparatus = cisternae sorts proteins =>glycoproteins, and lipids.
Lysosomes hold enzymes and produced by Golgi apparatus. Role in autolysis /exocytosis /pinocytosis
/endocytosis along with vesicles.
Endoplasmic Reticulum = Smooth ER which manufactures steroids and lipids and RER which
manufactures proteins
Nucleus holds genetic information DNA molecules. Surrounded by nuclear envelope that separates the
nucleoplasm from the cytoplasm and has nuclear pores allow mRNA out, nucleotides in.
Cytoplasm is the ground substance between organelles made of cytosol with dissolved substances within it
Mitochondria are the site of most chemical reactions where Kreb’s cycle and oxidative phosphorylation take
place. Greatly folded inner membrane (cristae =large suface area)
Ribosomes made of rRNA and tRNA and play important role in protein synthesis
Cell membrane = partially permeable, allows selective diffusion. Consists of phosholipid bilayer. Proteins in
membrane = carriers for facilitated diffusion and active transport, protein channels for charged ions,
enzymes, proteins with carbohydrates attached for cell to cell recognition, specific protein receptor sites for
antigen/hormones.
ADAPTATIONS OF OTHER IN ANIMALS RELATED TO FUNCTION
Link with Nerve cells have sodium-potassium ATPase proton pumps in membranes made of protein which
pump ions to maintain a negative resting potential and voltage gated pumps in membrane which pump ions
to generate an action potential. Two types of neurone: sensory and motor which have cell body in a different
place. Some have myelin sheath=>saltatory conduction which speeds up transmission of impulses,
drendites, axon, axoplasm, Nodes of Ranvier motor end plate etc.
Post synaptic membranes have protein receptor sites for neurotransmitters
Muscle cells act as effectors, receiving neurotransmitters at neuromuscular junctions and contain myofibrils
made of actin and myosin filaments. Have sarcolemma, sarcoplasm, sarcoplasmic reticulum and more than
one nucleus. Discuss how these structures enable the muscle cell to fulfil its role.
White blood cells defend against disease. Agranulocytes have non-granular cytoplasm and compact
nucleus- some ingest bacteria whilst others produce antibodies. Granulocytes have granular cytoplasm,
lobed nucleus, engulf bacteria by phagocytosis.
Red blood cells have no nucleus so that there is more space to hold haemoglobin molecules to carry
oxygen around the body Biconcave disc shape for large surface area and flexible.
Epithelial cells in alimentary canal- in stomach, ileum have microvilli. They have enzymes embedded in
cell surface membrane e.g. sucrase, maltase etc., large no. of mitochondria, blood vessels and lymphatic
vessel.
Hepatocytes also have microvilli and large no. of mitochondria for respiration and lots of SER for fat
metabolism and a prominent nucleus for protein metabolism and control. Also lots of lysosomes for
detoxification. Cells in the placenta and some tubule cells in the kidney have microvilli too=> increases rate
of absorption and exchange
Eyes have sensory cells connected to optic nerve. Cone cells hold one of three types of Iodopsin and are
responsible for visual acuity. Each cell connected to one bipolar neurone. Rod cells contain Rhodopsin and
are responsible for visual sensitivity.
Sperm cells/ secondary oocyte.
Podocytes provide filtration slits in the renal capsule.
PLANT CELLS
Structures not in animal cells:Cell wall made of cellulose fibres. Provides support for herbaceous plants because when water enters the
cells through osmosis the cell wall does not expand and therefore the cell becomes turgid and also gives
direct support to the cell. This can not happen in animal cells due to no cell wall. Partially permeable due to
gaps in wall.
Chloroplasts trap light energy= site of light dependent and independent photosynthesis reactions. Consist
of grana, thylakoid membrane (where chlorophyll molecules are found), stroma (liquid part)
Vacuole contains cell sap consisting of amino acids and is surrounded by a membrane- acts as a temporary
food store. Takes up most of cell.
Plamodesmata = string of cytoplasm that connects cells and provides symplast pathway for water in root
hair cells
Middle Lamella is made of pectin and is between cell walls of neighbouring plant cells
Plant cells also have endoplasmic reticulum (smooth and rough), plasma membrane, nucleus, mitochondria
and golgi apparatus
Palisade cells = major site of photosynthesis on the upper part of leaves there fore have a large number of
chloroplasts
Spongy mesophyll cells = site of gas exchange
Upper epidermal cells = protect against water loss and have hairs to trap water, transparent cells.
Phloem (removes products of photosynthesis, carries sucrose, amino acids, minerals ions, vitamins)
consists of:
*Sieve tube cells which have cellulose cell walls, a few organelles along the wall, but no nucleus, Golgi
apparatus or ribosomes. Sieve plates at end of cell has holes in it.
*Companion cells which are next to sieves tube elements with all the cell organelles so supply energy
for the sieve tube cells
Xylem cells have lignin around them and are dead and have lost end cell wall. Carry water up plant and
provide support.
Guard cells control water loss and allow enough carbon dioxide in for photosynthesis. Kidney bean shape
as inner cell wall is made of thicker cellulose than outer cell wall. Have proton pumps made of the protein
ATPase in their membrane to pump K+ ions in/out.
Also parenchyma cells= packing tissue/storage, collenchyma cells=provide support, Sclerenchyma
cells=dead cells made of lignin.
Root hair cells which provide a large surface area for diffusion