Cell Size & Function PDF

## Cell Size & Function - Why cells are so small: Diffusion over long distances is slow, minimizing the distance for access to oxygen, substances, nutrients, etc. is faster. - Plant structure & specilization: - Four organs in plants: roots, stem, leaf, flower - Photosynthesis occurs in chl...

## Cell Size & Function - Why cells are so small: Diffusion over long distances is slow, minimizing the distance for access to oxygen, substances, nutrients, etc. is faster. - Plant structure & specilization: - Four organs in plants: roots, stem, leaf, flower - Photosynthesis occurs in chloroplasts of plant cells: 6CO₂ + 6H2O + light (energy) -> C6H12O6 + 6O2 - Cellular respiration occurs in mitochondria of cells: C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP) ## Parts of a Leaf Cell - **Epidermal tissue:** Flat single layer of cells on upper/lower leaf. - Protects leaf, has no chloroplasts. Cuticle: a clear layer prevents evaporation through the tissue. - **Palisade tissue:** Long narrow columns of cells under epidermal tissue. - Main area of photosynthesis, has chloroplasts. - **Spongy tissue:** Round, loosely packed cells under palisade tissue. - Main area of water/gas exchange, minor photosynthesis, some chloroplasts. - **Stomata:** Tiny openings on the bottom of the leaf. Allows the exchange of CO2, O2, H2O. - **Guard Cells:** Cover stomata to allow substances in/out. - **Vascular Tissue:** Tubes arranged in vascular bundles. - Xylem: carries water/minerals from roots to leaves. - Phloem: carries sugars from leaves to the rest of the plant. ## Vesicle Mediated Transport - Used to facilitate movement of substances. - **Endocytosis:** Membrane forms a pocket around the substance the cell wants to take in. Transports particles to specific parts of the cell. Types: - **Phagocytosis:** Takes in large solid particles. - **Pinocytosis:** Takes in small fluid droplets. - **Receptor-mediated endocytosis:** Receptors bind to compounds & take them in. - **Exocytosis:** The reverse of endocytosis. Vesicles fuse with the membrane and eliminate particles out of the cell. ## Tonicity - The ability of a solution to move water in/out of a cell through osmosis. - Comparison of the amount of water inside to outside the cell. **Key Terms:** - **Solute:** Substance that dissolves. - **Solvent:** Substance that does dissolving. - **Solution:** Solute + Solvent together. - **Hypotonic:** Solute inside the cell is greater than outside, causing water to move into the cell (cell swells up/bursts). - **Hypertonic:** Solute outside the cell is greater than inside, causing water to leave the cell (cell shrinks/shrivels). - **Isotonic:** Solute inside and outside is equal, causing water to move in/out equally. - **Tonicity of the cell is always opposite to the tonicity of the solution.** - Hypotonic cell = hypertonic solution. ## Water & Sugar Transport - **Adhesion:** Attraction of water molecules to other substances molecules. - **Cohesion:** Attraction of water molecules to other water molecules. - **Capillary action:** The ability of water to cling to the surface of a solid. Water moves upwards. ## Water transport - **Root hairs:** Increase surface area for absorbing water and dissolved minerals. - **Water enters root cells by osmosis:** Minerals travel via active transport. - **Solution of water & minerals is zylem sap.** - **Zylem vessels:** Dead hallowed out cells, carry zylem sap up to stems/leaves. **Root pressure pushes as water moves in root cells from osmosis.** - Pressure builds up. Water moves from high to low pressure in roots. **Transpiration pulls:** Evaporation of water through stomata/lenticels pulls water up the stem into leaves. Pulls up water molecules next to root pressure/transpiration. Uses cohesion/adhesion. ## Sugar transport - Sugars are translocated through phloem. Sugars are translocated to stems and roots by phloem vessels. - **Phloem vessels:** Living cells (sieve tubes) connected by sieve plates. - **Companion cells:** Lie alongside sieve tubes offering support. - **Sugar/minerals enter phloem from active transport called phloem sap.**