The Life of Plants

Plants are Autotrophs What does this mean? They have the ability to convert inorganic material to organic material. Make their own food!

The need for oxygen Aerobic Organisms: Organisms that require oxygen for cellular respiration. Cellular Respiration Equation: C6H12O6 (s) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (l) + heat Photosynthesis Equation: 6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2

Balancing the Equations Generally in green plants during the day Rate of Photosynthesis > Rate of Cellular Respiration More Carbon Dioxide used in photosynthesis than produced by cellular respiration. Oxygen produced used in cellular respiration, remaining diffuses out of the leaf into the environment as waste. Cellular Respiration Equation: C6H12O6 (s) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (l) + heat Photosynthesis Equation: 6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2

What happens when the lights are turned out? At night, photosynthesis doesn’t occur. Rate of Cellular Respiration > Rate of Photosynthesis O2 is taken in and CO2 is released. CO2 and O2 can be both nutrients and waste products.

Gas Exchange in Plants Most don’t have specialised gas exchange organs. Simple plants have extremely thin leaves, often one cell thick. Why? High Surface Area Small distance for Oxygen to travel via diffusion

Gas Exchange in Plants Vascular plants: Land plants have specialised tissues for transporting materials. Complex. Plant cells are loosely packed, area between cells filled with air allowing rapid diffusion. Why? Increased Surface Area for diffusion to occur. Cells are organised near the surface, even in large plants Why? Less distance to travel Cells are covered with a thin film of water. Why? Moist area required for diffusion

Stomata Gas exchange occurs via diffusion through special openings called stomata Open and close to regulate gas exchange Positioned in relation to plant’s environment. Water lilies: confined to the upper epidermis Eucalypts: adapted to dry conditions, stomata in sunken pits in the surface of the leaves. Reduces air flow across them lowering water loss.

Stomata Gas exchange in leaves occurs through stomata. Water enters guard cells, they expand, opening the stoma. Guard cells expand lengthwise because they have a thickened inner cell wall with cellulose fibres that prevent the cells expanding in width.

Stomata Terrestrial plants, must keep the water loss via evaporation to a minimum. Moist surfaces used for gas exchange are the major site of water loss. Stomata balance the need to bring in CO2 but close to prevent the plant drying out. Stomata close during the day if it is hot and dry. Prevents excessive water loss, but also drastically reduces the rate of photosynthesis.

Gas Exchange in stems and roots Stems also contain stomata. Woody stems and mature roots have a layer of waterproof and airproof cork cells. Air can pass through to cells beneath to loosely packed cells. Roots exchange gases with the air in spaces in the soil. Oxygen diffuses the moisture surrounding root hairs, then into the roots themselves. Waterlogged soil due to excessive rain or poor drainage, means spaces in the soil are filled with water instead of air. What happens if you overwater a plant? Less Oxygen in water than air, so overwatering can suffocate plants. Killed with kindness!

Transport in Plants If the plant is too big to transport only by diffusion, they require more complex tissues. Evolution increased the height and size of leaves. Increased the distance between the roots where water and nutrients were obtained and the leaves. Water, sugars and inorganic nutrients need to be transported.

Plant Transport Structures The Vascular Tissues: Xylem: Transports water and inorganic nutrients up from the soil. Long water filled tube of cells that have disintegrated leaving only their thick cell walls. Phloem: Transports sugars produced by photosynthesis throughout the plant. Sieve tubes of elongated cells. Are alive, with no nucleus or hard cell wall. Both are tubular structures that run continuously through roots, stems and leaves.

Xylem and Phloem

Xylem and Phloem

Water Uptake in Plants Dissolved nutrient ions taken into roots via active transport. Concentration of ions in roots high compared to outside. The water comes into the roots to balance the concentrations Passive movement of water by diffusion = Osmosis Aided by structure of fine root hairs = High Surface Area

Water Uptake in Plants Movement in Xylem driven by transpiration (loss of water vapour from leaves). Needs no energy, evaporation driven by the sun. Draws more water molecules upwards. Movement of organic materials (e.g. amino acids and sugars) through the Phloem is called translocation

How do plants remove their wastes? Extracellular fluids in plants is not regulated in the same way that the extracellular environment of animals is regulated. Plants generally do not have specialised excretory organs because: Low rates of metabolism much of their waste is gaseous, they reuse carbon dioxide in photo-synthesis and oxygen in cellular respiration capable of recycling much of their own nitrogenous waste—nitrogenous compounds produced from the breakdown of protein can be recycled into new amino acids less turnover of protein in plants, most of the structural components of plants are carbohydrates, whereas in animals they are proteins.

How do plants remove their wastes? Plants living in a large volume of water can simply excrete waste into the surrounding water. In terrestrial plants waste products such as salts and organic acids are simply stored within the plant. E.g. Deciduous trees deposit wastes into leaves causing colouration before being shed in autumn. Vacuoles are a 'dumping site' for metabolic toxic substances. Plus side is they make the plant unpalatable, so also works as a defence mechanism