Lecture 7: Producers & Plant Adaptations to the Environment PDF

Lecture 7 Producers & Plant adaptations to the environment  Producers / Autotrophs Producers are organisms that produce food for themselves and other organisms. They use light energy and simple inorganic molecules to make organic compounds. Producers are vital to ecosystems because al...

Lecture 7 Producers & Plant adaptations to the environment  Producers / Autotrophs Producers are organisms that produce food for themselves and other organisms. They use light energy and simple inorganic molecules to make organic compounds. Producers are vital to ecosystems because all organisms need organic molecules. Producers are also called autotrophs. There are 2 types: photoautotrophs and chemoautotrophs. Most 1.Photoautotrophs use energy from plants, sunlight to make food by photosynthesis. Some algae, and bacteria certain and also 2.Chemoautotrophs use energy from bacteria archaea chemical compounds to make food by chemosynthesis. review Prokaryotes: Metabolic diversity Chemoautotrophs in Hydro- thermal vent ecosystem (Deep Ocean Floor) PHOTOsynthesis: CHEMOsynthesis: Energy from the SUN + 3H2S+ 6CO2+6H2O + → 6CO2+6H2O → C6H12O6 (sugar) + 3H2SO4 C6H12O6 (sugar) + 6O2  Biological Classification Domains of Life Biologists classify living Protist organisms into a few large groups called DOMAINS Plants Producers can be found in all 3 domains * *some archaea are capable of photosynthesis, although their mechanisms differ from those of bacteria and plants Main Types of Photoautotrophs  Some Bacteria are Producers example of bacterial Producers - Cyanobacteria Cyanobacteria were formerly called blue-green algae due to their green and blue photosynthetic pigments They were once classified as blue-green Algae, because they grow in long filaments resembling algae, but are now considered bacteria because they lack a membrane-bound nucleus and chloroplasts. Photosynthesis in cyanobacteria (use C02 + light, make sugar and release Fixed (organic) carbon oxygen!)  Protists heterogeneous group of eukaryotic organisms Protists have evolved diverse cell structures, ecological roles, and life histories Protists vary in size, structure, mode of locomotion, and reproduction – Most protists are motile (some are sessile) – Reproduction ranges from asexual to sexual modes – Many protists are aquatic (terrestrial protists are found in moist environments) – Unicellular to multicellular Protists may be autotrophic, heterotrophic or mixotrophic Protists can be divided into 3 ecological categories Protists are more diverse than all other eukaryotes 1) Animal-like / heterotrophic 2) Fungus-like / heterotrophic 3) Plant-like / autotrophic = PRODUCERS Fungus-like Plant-like Animal-like, absorptive (photosynthetic) ingestive ex. Amoeba ex. algae ex. water molds Protists Producers: Algae single-celled algae There are unicellular and multicellular forms Freshwater or marine forms. They are photosynthetic organisms. 30-50% of atmospheric oxygen produced by algae Brown and red alae multicellular green algae  Ecological Importance of (Producer) Protists Play a key Role in aquatic food chains: Phytoplankton are the basis of food chains in freshwater & marine environments. (form foundation of food webs (use light energy to convert CO2 to organic compounds)) Aquatic Environments: Producers - Very abundant (1ml pond water ~500 single celled protists) Photosynthetic organisms: leading producers in oceans Zooplankton: Non- Scientists estimate that photosynthetic plankton roughly 30% of the (includes non-photosynthetic world’s photosynthesis protists along with many other is performed by organisms) diatoms, dinoflagellates, algae and other aquatic Phytoplankton: photosynthetic protists plankton (algae is a major Release oxygen component) What is a Plant? Multicellular Eukaryotic Terrestrial (most) Non-motile Cells have cell walls made of cellulose Most contain chlorophyll (green pigment) and produce own organic compounds (autotrophic)  Plants Ecological Importance: can perform photosynthesis Photosynthesis: Inorganic C Organic C Chloroplast is an organelle that contains the photosynthetic pigment chlorophyll chloroplast  Plants Ecological Importance: producers Plants are the basis of Terrestrial Food Chains Virtually every organism on land depends on plants for food, either directly or indirectly.  Plants Ecological Importance Reduce greenhouse gasses Plants moderate climate (shade) Plants provide cover/habitat for wildlife  Plants Ecological Importance Plants build soil (accumulation of dead plant material) Plants hold water Plants hold soil (forests prevent soil erosion) Soil erosion is often a result of forest clearing. When there are no trees covering the soil, rainfall lands directly on the ground, rather than dripping gradually through the tree branches and falling much more softly to the forest floor. This means that when it rains, more water hits the ground with more force, washing soil away. Root systems also act as underground nets preventing extensive soil movements.  Human Welfare depends greatly on seed plants No group of plants is more important to human survival than seed plants Most food comes from angiosperms Six crops (wheat, rice, maize, potatoes, cassava, and sweet potatoes) yield 80% of the calories consumed by humans Plants also feed livestock Modern crops products of relatively recent genetic change from artificial selection Medicines derived from plants Recall…  Plant adaptations to biomes / their environment Recall: Limitations of resources helps explain differential survival & reproduction, which lie at the heart for natural selection Important resources for plants: Light & water Energy Requirement: Light - Most plants take in energy thru photosynthesis (capture light energy from the sun) Factors affecting light availability: o light is more diffuse at higher latitudes o Sunlight available during the day o Not available in all seasons in many biomes o Some plants grow in the shade of surrounding plants Water is critical for life In terrestrial environments organisms need to minimize water loss  Plant Adaptations to Biomes For photosynthesis plants need to acquire CO2 via STOMATA STOMATA: tiny pores on leaf surface that facilitate gas exchange Stomata are formed by pairs of guard cells which are like 2 water filled ballons joined at both ends Water IN = cells swell = stomata open Stomata OPEN Stomata CLOSED Water evaporates, guard cells get smaller = stomata close  Anatomy of Leaves Leaves are organs that increase the surface area of vascular plants to capture light. o The outermost layer, called the cuticle, is a waxy coating that helps prevent water loss. o Beneath the cuticle lies the epidermis, which protects the leaf and facilitates gas exchange through small openings called stomata. The mesophyll, located in the middle of the leaf, is where most photosynthesis occurs – it contains two types of cells: palisade mesophyll, which is densely packed with chloroplasts for maximum light absorption, and spongy mesophyll, which has air spaces that facilitate gas exchange. The leaf also contains vascular tissues that transport water (xylem) and nutrients (phloem) and surrounded by specialized plant cells called the bundle sheath cells.  C3 Photosynthesis - overview Photosynthesis: Solar energy used to build sugars. These sugars are used for cellular respiration, plant growth & reproduction The plant combines CO2 with a 5-carbon molecule (RuBP) to make two 3C molecules of PGA. PGA (3C) is then used to make glucose & other sugars. This type of photosynthesis is called C3 C3 photosynthesis takes place in the mesophyll cells, just past the leaf 3C surface, with direct access to the stomata. The expensive part in terms of water comes in at the start of the process when the stomata open-up to capture CO2.  Trade-off between water & energy When guard cells swell & open, CO2 enters leaf -> hardly any energy expenditure BUT although low energy to open stomata it leads to “expensive” water loss! Stomata OPEN Stomata open – water evaporates from leaf o Plants lose ~ 100-500 molecules of water for each molecule of CO2 molecule they acquire o Therefore, strong selective pressure in DRY environments!  Enzyme essential at converting CO2 to PGA (Rubisco) not good at its job! When CO2 level low or temperatures are high, the enzyme cannot distinguish CO2 from O2 (enzyme uses O2 instead!), therefore this reduces photosynthetic efficiency. o This may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2 Under Cool, Moist conditions = no major issues ~ 90% of worlds’ plant use this type of photosynthesis (called C3 photosynthesis) enzyme But this type of photosynthesis is not efficient in dry hot environments 2 other forms of photosynthesis have Photosynthesis Not Efficient – evolved in drier efficient! waste of energy! environment  C4 photosynthesis spatially separates photosynthetic steps to increase efficiency In C3 plants CO2 capture & sugar creation occurs in the same cell type just inside of stomata (mesophyll cells) When C4 plants take in PGA (3C) CO2 they combine the CO2 with PEP to make a 4C molecule (hence C4) that is moved to the bundle sheath cells away from stomata. Moves C4 molecule to cells lower down, it releases CO2 then used to make sugar  C4 photosynthesis ↓[CO2] spatially separates photosynthesis In the lower bundle sheath cells, the C4 molecule releases CO2 So, the concentration of CO2 remains high, enzyme uses CO2 (not O2) and photosynthesis remains efficient CO 2 concentration remains high in lower cells so that enzyme works well! CO2 gradient remains low in upper cells, so CO2 keeps coming in when stomata open, Keeping the concentration of CO2 low in ↑[CO2] upper cells speeds up CO2 acquisition and leads to LESS time with open stomata (reduce water loss!) Common in grasslands (found in approximately 3% of the world’s plant species).  CAM photosynthesis evolved in extremely DRY conditions In desert it may be dangerous to open stomata at all during the heat of the day! CAM method involves temporal separation of getting Night CO2 and making sugars. Stomata open In this method CAM plants open stomata only at night, when evaporation is lowest & take in as much CO 2 only at night! During the day, stomata stay closed! Use CO2 To keep low CO2 concentration in cells at night (so that to make it can keep coming in down its concentration gradient) Day sugars plants combine CO2 with a 3C molecule to make a 4- carbon molecule. Day: stomata close and plants break down C4 into CO2 so that they can proceed with photosynthesis and make sugars.  C3 C4 CAM Biome Mostly Tropical, Desert / Arid Temperate semitropical, grasslands Conditions cool, moist hot Very hot / desert C4 plants most frequent in grasslands  Ability to acquire water Roots to shoot ratio Drier biomes water is much shorter supply than light Roots reach down toward water – leaves reach up to capture light Plants can alter their investment in each of these depending on the availability of water & sunlight To compare these allocations, we can compare the biomass of the plant roots to the biomass of its leaves and stems (shoots) to examine root to shoots ratios o A high root to shoot ratio (>1) suggest large investment in root growth (investing in acquiring water) o Low ratio (