Lecture #8……… Angiosperms: Form & Function
Plant cells • contain all the usual eukaryotic “ suspects ” – mitochondria, Golgi (dictysomes), ER, vacuoles etc…. – double phospholipid plasma membrane with embedded proteins and carbohydrates – BUT they also possess a cell wall – cytoplasm and the organelles are sometimes referred to as the protoplasm or the protoplast (single plant cell) – nucleus is similar to the animal cell nucleus
Plant cells • unlike animal cells – plant cells are capable of storing large quantities of many substances • some substances are stored within the cytoplasm – tannins, phenols, silica – calcium oxalate crystals
Plant Vacuoles • other materials are stored within vacuoles • primary central vacuole – water and salts and wastes • increasing the size of this vacuole can rapidly expand the size of the cell without the need to make more protoplasm • in seed plants – this vacuole becomes a storage depot for starches required for embryonic growth • spherosomes or lipid bodies - lipid
Plastids • plant cells also possess specialized structures known as plastids – plastids = group of dynamic organelles that are able to perform many functions • made of an inner membrane and an outer membrane with a stroma in between – many similarities to a mitochondria • several types within a plant cell
1. Chloroplasts • form from immature pro-plastids once the cell is exposed to light – contain the photosynthetic pigment chlorophyll and all the accessory proteins and complexes required for photosynthesis – inner membrane is elaborately folded into membrane sheets called thylakoid membranes (large surface area for photosynthetic machinery) – in certain areas the thylakoid membranes is folded into vesicle- like bags stacked together – grana (transport of H+ ions required in photosynthesis)
Other Plastids • 2. amyloplasts – in plants tissues that can’t photosynthesize – roots, bark and wood cells – accumulate sugar and store it as starch • 3. chromoplasts – e.g. in tomatoes and yellow squash – bright red, yellow and orange lipids accumulated here • 4. leucoplasts – large and unpigmented plastids – no chlorophyll or lipid pigments – involved in the synthesis of fats and phospholipids potato amyloplasts tomato chromoplasts
The Cell Wall • all cells of the plant have cell walls (except the sperm) • an active, dynamic organelle with many metabolic functions • contains large amounts of cellulose – in the form of cellulose microfibrils = 10 to 25 nm wide – made by rosette protein complexes
The Cell Wall • all cells have a thin primary cell wall • made of cellulose • also contains pectin = a complex polysaccharide that allows for plant growth • pectin also forms the middle lamina found between two plant cells middle lamina – “cement”-like layer of pectin found between two plant cells
The Cell Wall • in cells that require strength – there is a thicker secondary wall that is
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- Spring '14