Plant Biology Past Paper PDF

*Please note that for ck402 this group is classed as group 1 Campbell & Reece is a main area of study/research for this module. Plant Blindness- plant biomass dominates the total biomass of the Earth. Approximately 450 Gt of the total 550 Gt Reasons why plants are relevant 1. Climate Chang...

*Please note that for ck402 this group is classed as group 1 Campbell & Reece is a main area of study/research for this module. Plant Blindness- plant biomass dominates the total biomass of the Earth. Approximately 450 Gt of the total 550 Gt Reasons why plants are relevant 1. Climate Change 2. Sustainability 3. Food Supply 4. Biodiversity 5. Pollution History of Studying Plants Phytochemicals- medicine Scurvy- vitamin C deficiency causing the tissue in the gums to become rotten. Orto Botanica di Padova- a botany garden founded in 1545 Dioscorides- Greek in the Roman Empire that created the De Materia Medica which contains a detailed pharmacology of plants. Was the most important reference work from 70AD to the 1600s Culpeper- from 1616 to 1654, wrote a detailed pharmacology of plants and their uses Modern History Four Global Crops- maize, rice, wheat, and soybean are 2/3 worlds agricultural produce. It’s clear that climate change has decreased the yield of these crops massively and therefore plants must be carefully studied and monitored for a a sustainable future Why Study Plants 1. Medicine 2. Food 3. Materials i.e. Velcro is inspired by gallium aparine 4. Energy 5. Bioremediation fish waste is a resource for growth duckweed (Lemna) 6. Carbon Sinks 7. Human Health 8. Social Policy Bioremediation has averted 1,900 deaths a year in the UK alone 1 Plant Structure Cytology- study of the cellular structure. Plasmodenta- links plant cells allowing them to act as a multicellular unit rather than a unicellular one Histology- study of the structure of the tissue Must know the transverse sectional structure of a dicot leaf Organ- collection of tissues that together carry out a particular function i.e. root, shoot, and leaf Anatomy- study of the entire internal structure of an organism Morphology- study of the entire external structure of an organism Do not worry about Latin plant names or notes in photos!!! Function of the Structure Example- see page 38 of slides Answer- different structures have met different criteria in order for numerous functions to occur within an organism Examples for link structure- function Nucleus- protect DNA Chloroplast- photosynthesis Peroxisomes- oxidative metabolism. Glyoxisomes- lipid metabolism 2 Study Plant Structure Taxonomy- identifying, grouping & naming organisms Theophrastus- father of botany. He wrote Historia de Plantis which described 4 taxonomic groups- trees, shrubs, under shrubs and herbs Carl Von Linne- see notes from BL1002 Determinants of Plant Structure Plants that share the same pressure exerted by their environment they will share morphological traits Genetic Adaptation also known as natural selection Convergent Evolution- evolution of similar traits due to environmental pressure Analogous Traits- similarities between organisms that are not present in the last common ancestor i.e. see cacti vs a spurge Plasticity- the ability of an individual plant to adjust structure to local environment Heterophylly- within organisms, in principle, all cells are genetically identical. For example, in some plants underwater leaves streamline and surface leaves float to adapt to living in aquatic environments Why is plasticity more common in plants Plants are sessile Animals are mostly mobile Plants need to adjust to local unfavourable conditions Numbers of Plants 25000 Mosses 14000 Ferns 900 Gymnosperms 250000 Angiosperms 3 Plant Organs Tissue- group of cells with common structure and function Dermal Tissue- single layer (epidermis) Vascular Tissue- xylem and phloem Ground Tissue- parenchyma Meristem Tissue Plants are totipotent- all cells can dedifferentiate divide and develop into completely new organisms This is a part of environmental plasticity in plants Originally animals were seen as unipotent Pluripotent stem cells however can develop into different tissues but not a whole organism But with technology advancing it may become possible Leaf In essence the carpel and stamen are rolled up leaves The sepal is also known as a leaf Leaves play a role in both photosynthesis and reproduction However, it may also play a role in storage i.e. onions and cactus 4 Leaf Structure Epidermis Waxy Cuticle- prevents dehydration Stomata- gas exchange Trichomes (hairs) Mesophyll Spongy Parenchyma- helps absorb carbon dioxide Palisade Parenchyma- Vascular System Phloem- transports sugars Xylem- transports water Stem Structure Carries leaves and positions them in the light Controls stem length Connects the root to the leaf allowing for exchange of substances Like leaves there is also modified stems i.e. cacti have modified stems that can photosynthesise, and potatoes are modified to store food Apex- bud with meristem (dominance) Nose & Internode Axillary buds (most dormant) Apical Dominance occurs due to an evolutionary adaptation allowing plants to grow longer to reach light for photosynthesis If there is no apical dominance witch’s brooms form The stem contains an epidermis, ground tissue (containing a pith in the centre, cortex outside vascular bundles and fibres) and vascular tissue (located behind the epidermis) 5 Collenchyma- found in young tissue & is living & flexible. Sclerenchyma- found in mature tissue & is dead & rigid i.e. linen and hemp Roots Structure Anchors, uptake water & minerals, storage and photosynthesis Lateral roots from the sides of the main root Adventitious roots from the stem i.e. mangroves Tap roots i.e. carrots Photosynthesis can occur in the leaves (most common), stems (phylloclade) and roots (i.e. American ghost orchids) due to plasticity! Roots are beneficial as part of the ecosystem i.e. mycorrhiza are mutually beneficial networks of plants and fungi. Root Hairs- extension of epidermal cell increasing uptake surface for absorption of water and minerals. Lateral Roots- multicellular root The roots also contain vascular tissue (located in the centre of the root), ground tissue and an epidermis 6 Endodermis- inner layer cortex that controls nutrient uptake Pericycle- may become meristematic and forms the lateral root. Lateral shoots pre-formed (axillary buds) Dormancy axillary buds controlled by apex Located near surface stem (near vascular system) Lateral roots not pre-formed Located deep inside (near vascular system) Primary Growth Processes responsible for this include mitosis and cell enlargement These are followed by cell differentiation Mitosis occurs in the meristem in roots and the stem apex in axillary buds. Meristem contains embryonic cells Cell division in the meristem results in initials (which remain in the meristem) and derivatives (which will go on to differentiate) There in indeterminate growth in roots and shoots and determinate growth in leaves Determinate growth stops when the organ(ism) reaches a certain height Annual- from germination to seed production within one-year (includes major crops) Biennials-from germination to seed production in 2 years Perennials- long lived species. Bristlecone Pines- 5000 years Yew Tree- 2000 years 7 Secondary Growth Thickening of roots and shoots in woody plants Development secondary meristems i.e. vascular cambium and cork cambium Vascular Cambium develops between the xylem & phloem and is a cylinder of meristematic cells. Its main function is to produce more xylem and phloem. They activate during the summer and remain dormant during the winter. In the spring they form large diameter xylem and, in the autumn and summer they form smaller diameter xylem. Woody plants develop year rings which vary based on time and weather conditions and help estimate their age Old xylem is non-functional as it is a heartwood stuffed with preservatives or is completely absent Young xylem = sapwood Old phloem disintegrates Periderm- cork cambium and cork Bark- phloem and periderm Bark- all tissues external from the vascular cambium Trees will survive cork removal Removal of bark means certain death 8 Photosynthesis Over 2 billion years ago, oxygen was very rare Carbon dioxide and water form carbonic acid Iron in the lithosphere is oxidised due to photosynthesis Autotrophs- use inorganic forms of carbon and require energy to reduce carbon dioxide into organic carbon. Heterotrophs- requires a supply of organic carbon, depends on dead or living organic matter and obtain energy and oxidises carbon to form carbon dioxide (released during respiration) An exception to this rule is the broomrape, a parasitic plant that obtains its nutrients through the grass surrounding it. Another example is the Elysia chlorotica, a sea slug that photosynthesises with the help of algal chloroplasts. Kleptoplasty- the behaviour whereby an animal takes chloroplasts from a food source and incorporates these into the tissues of their own digestive tract. Photo autotrophs- use light energy Chemo autotrophs- use chemical energy by oxidation of sulfiric acid, iron, etc… Photosynthesis- conversion of carbon dioxide and water into glucose and oxygen converting light energy into chemical energy. Why do chloroplasts have a bilayer? Endosymbiosis of plants with fungi caused the unicellular photosynthesising algal cell to combine with the heterotrophic host cell. Chloroplast Components Double membrane ctDNA Thylakoid membranes Grana Internal Lumen Stroma Chlorophyll 9 Understanding Photosynthesis Jan Baptist Van Helmont questioned whether soil was a source of biomass in the 1640s. He tested by weighing plants and their change in weight after 5 years He concluded that biomass is derived from water (not entirely correct) Another man Joseph Priestly discovered a concept of good and bad air (dephlogisticated) and is known as the father of the soft drink Chlorophyll and Light Absorption photon (package of energy) Chlorophyll gets in an excited state when energy is captured Chlorophyll falls back to ground state and the energy is released as heat or fluorescence Light energy is captured and converted into chemical energy Photosynthesis There are two stages in photosynthesis, light reactions, and the Calvin cycle. Light Reaction- conversion of light energy into chemical energy (ATP and NADPH) Dark Cycle (Calvin Cycle)- incorporation of carbon dioxide into sugar with energy produced in light reactions. Light Reactions Redox Process Transfer of electrons from a donor (water) to an acceptor molecule with a lower redox potential. Requires energy Process is driven by energy from absorbed photons of light. Photosystems- consists of chlorophyll organised as light harvesting complexes, a reaction centre that catalysed a charge separation and primary electron acceptor. 10  Non-Cyclic Electron Flow Photosystem II charges separation Transfer electron to the primary electron acceptor and onwards to Photosystem I Re-reduction PSII by electron from water Photosystem I charge separation Transfer electron to the primary electron acceptor and onwards to NADP+ Re-reduction PSI by electron from PSII Products of Light Reactions NADPH- a form of reducing energy i.e. energy plus electrons Water splits into four hydrogen ions, an oxygen molecule and four electrons. ATP ATP Synthesis Energy stored as a proton gradient This is used to drive ATP synthesis by ATP synthase. Chemiosmosis- movement of protons across a semi permeable membrane against an electrochemical gradient. This drives photo phosphorylation. Calvin Cycle Carbon fixation Carbon dioxide is linked to ribulose biphosphate forming ribulose biphosphate carboxylase. A five-carbon sugar and a single carbon sugar bond to from two three carbon sugars as a six-carbon molecule is far too unstable. Phosphorylation and Reduction The three-carbon molecules are phosphorylated using ATP The three-carbon molecules are reduced by NADPH These molecules can then be converted in glucose and numerous other sugars. 11 Regeneration Acceptor Molecule Ribulose Biphosphate Five three-carbon molecules are used to form three five-carbon molecules The result is the recycling of the carbon skeleton than can incorporate carbon dioxide. C4 Metabolism Adaptations that increase carbon dioxide levels in leaves without increasing transpiration. Adaptations that gather all available carbon dioxide in a small group of cells. The Calvin cycle is prefaced by a C4 cycle. C4 linked Leaf Anatomy Bundle sheath cells fixate carbon dioxide throughout the Calvin Cycle Rest of mesophyll collects carbon dioxide and transports it as a C4 to the bundle sheath. C4 Metabolism Carbon dioxide is bound to phosphoenolpyruvate to form phosphoenolpyruvate carboxylase. PEP and PEPC C3 +CO2 = C4 C4 transported to the bundle sheath CO2 released in bundle sheath cells C3 returned to mesophyll (cycle) Why does it work? PEPC can work at low CO2 (has a high affinity for CO2) Large catchment are for CO2 This working as a concentrating mechanism C4 Metabolism comes at a Cost Most C4 plants originate in hot, dry areas i.e maize and sugarcane CAM Metabolism Crasulaceae family acid metabolism C4 acids accumulate in vacuoles at night CO2 is released during the day This decreases water loss during dry or hot days Temporal rather than spatial separation of C3 and C4 metabolism 12 Respiration = Reverse of Photosynthesis 13 Plant Nutrition and Transport Stomatal Opening and Closing Compromise CO2 by uptake and transpiration Trade off = biological balancing act 90% of water loss in plants is through the stomata Stomata make up 1-2% of plants’ surface area It is important to note that the leaf has a waxy cuticle to prevent water loss Transpiration and its Benefits Keeps plants cool Transport route from root to shoot In extreme settings the plant can 10 to 15 degrees cooler than air temperature Cooling prevents cellular damage to biomolecules Altering balance transpiration vs CO2 uptake Environmental Plasticity; stomatal density is up to 20,000 per cm^2 (most seen in plants in high light environments) and indicates atmospheric CO2 on fossils and other historic samples. Regulation Stomata Genetic Adaptations; C4 and CAM photosynthesis Stoma Opening and Closing Swelling guard cells= opening Shrinking guard cells= closing Shrinking and swelling occur due to water uptake or loss Proton pump create change in membrane potential (voltage) over the membrane Potential drives potassium ion uptake and release through potassium channels This is an active process that costs ATP Passive water uptake occurs through aquaporins in the membrane Swelling/Shrinking= change in aperture Stoma Response to Environmental Signal Stoma mostly close in the dark (except CAM plants) Stoma regulated by its circadian clock Stoma open when internal CO2 is low Stoma close when turgor leaf decreases. 14 Mineral Nutrients Chemical elements absorbed through soil as inorganic ions Essential to completing life cycles Many different essential and non-essential mineral present 80-90% of plant fresh weight is water 96% dry weight is organic, and the rest is inorganic Essential Macronutrients include carbon, oxygen, hydrogen, nitrogen, phosphorus, sulphur, potassium, calcium, and magnesium Essential Micronutrients include chlorine, iron, manganese, boron, zinc, nickel, copper, and molybdenum. If concentration is super optimal than it can lead to toxicity Food Fortification 1/3 of the world are at risk of a zinc deficiency Approx 800,000 die from it every year Zinc is deficient in about half of the world’s agricultural soil Therefore, mineral uptake is as important for the plant as it is for us Nutrient Uptake by Roots Absorption Nutrient Root Hair Zone includes extension epidermal cells, large surface area and permeable epidermal tissue. Mycorrhizae- symbiotic structure including plant roots and fungal hyphae (large surface area) Fungi can be used to improve the quality of degraded soil, enabling pioneer plants to establish Apoplast- continuum formed by extracellular spaces in matrix of cells Chemical composition apoplastic fluids reflect soil. Apoplastic route blocked at the endodermis. Symplast- continuum of cytoplasm connected by plasmodesmata. Selective absorption of nutrients through a membrane Root hair and corte cells all absorb nutrients from the apoplastic fluid (large absorption area) Selective Uptake of Nutrients through the Symplast “Channels” selectively enable ions to cross the membrane into the cell. The membrane potential = the driving force Inside the cell is more negatively charged than the outside. 15  Uptake cations are driven by membrane potential and is enabled by the channels. Generation of membrane potential is done using ATP. Ions are transported through channels (or on rare occasions through the cell membrane itself) Channels/Channel Proteins- create a hydrophilic (polar) channel through the cell membrane, allowing for the transport of molecules down an electro-chemical gradient. Transporters & Co-Transporters Rate of nutrient uptake through carriers and channels do matter An example of this would be the nutrient release by fish (ammonia) must be matched by nutrient uptake rate plants or else they become toxic for the fish Endodermis (Selective Passage) Consist of a casparian strip- a belt of waxy material. It is found in the wall of endodermal cells It blocks the apoplastic route Forces water and nutrients through the symplast This results in a process known as selective uptake. Stele This is the tissue inwards from the endodermis Discharge of water and nutrients occur here through the vascular system (xylem) Transport of Water and Nutrients Xylem forms a contininuum, is dead when functional and has cell walls. Driving Force Xylem Transport 1.Root Pressure Upward Force Important when there is no transpiration i.e. humid, night and when a plant has no leaves. Osmotic forces create root pressure Salts accumulate in the stele by active transport This leads to the passive flow in of water by osmosis. Guttation- root pressure pushes out excess water through the leaves. 16 Transpirational Pull Transpiration creates negative water pressure and negative water potential. Cohesion between water molecules transmits pull from leaves to the roots. Cohesion is possible due to hydrogen bonding and the uninterrupted chain of water molecules. Phloem Transport Transport of sugars, amino acids and hormones. The main sugar transported is sucrose. The direction of phloem transport is variable. The source of substances for phloem transport includes where sugar is produced/released, photosynthesis, and when starch/oil is converted into sugars. The sink of where substances get used by the plant include respiration, oil/starch biosynthesis and other cellular forms of metabolism. Phloem Structure Sieve Tube Members are aligned, connected to each other, have a connection to the sieve plates and are alive (despite lacking a nucleus and ribosomes) The Companion Cell is linked through the plasmodesmata. Mechanism Phloem Transport At source: >Sugar accumulation in sieve tube > High concentrations, against sucrose gradient >Active, costs ATP >Passive uptake water (osmotic) >Generates positive pressure At sink: >Sugar removal from sieve tube >Sugar metabolised (ATP/NADPH) >Sugar converted into starch >Sugar to be used to synthesise cellulose >Passive loss water (osmotic) > Decrease pressure 17 Animal Respiration Gas Exchange- supplies oxygen for cellular respiration and disposed of carbon dioxide Cellular Respiration- a set of metabolic reactions and processes that take place in the cells of organisms that convert biochemical energy from nutrients to ATP and then release waste. Respiratory Medium- is the environment in which you obtain oxygen for respiration. General Functions of Respiration Gets oxygen to cells Gets rid of carbon dioxide Unusual groups simply different strategies in order to respirate Respiratory Organs Flatworm- body wall/ internal cavity Fish- gills, gill filaments and blood vessels Terrestrial Arthropod- spiracles, tracheoles and trachea Mammal- mammalian lung, trachea, alveoli, and blood vessels. Single Celled Organism Gas transfer occurs across the plasma membrane by simple diffusion in single called organism i.e. amoeba, a member of the Protozoa family. Small Vertebrates In small vertebrates i.e. flatworms, diffusion is adequate for the needs of the animal due to its size Important to Note In specialised organs, there are normal extensive patterns of invagination and evagination to increase the surface area of the membrane Gills are evaginated and lungs are invaginated Gills are branchial and lungs are pulmonary 18 Aquatic Creatures Starfish breathe with their tube feet as well as their gills (branchial papulae). Solitary papules are present on top of the starfish. Most oxygen is taken up from water that passes over their respiratory organs Fish In fish, due to low oxygen levels in the water, gills are adapted to remove more than 4/5 by counter current flow of blood and water. Fish also have organs with increased surface area. Counter current exchange is a mechanism occurring in nature, in which there is a crossover of some property, usually heat or some chemical, between two flowing bodies flowing in opposite directions to each other. Terrestrial Arthropods The tracheal systems of insects consist of tiny branching tubes that penetrate the body Air enters the trachea through openings called spiracles on the insect’s body surface This air then passes into smaller tubes called tracheoles. Tracheoles are closed and contain fluid When the animal is more active, most of the fluid is withdrawn into the body This increases surface area of air in contact with cells Larger insects use bellow like movements to pump air into the tracheal system Circulatory systems plays little to no role in respiratory needs Amphibians Larval amphibians- use gills and skin Most adult amphibians- use lungs and skin Gills do remain in some adults i.e. axolotls Some salamanders also lack lungs Birds Lungs are rigid structures that undergo slight change in volume Air sacs expand and contract Air flows unidirectionally Gas exchange system is cross current 19 Mammals Lungs of mammals are densely filled with branching airways These have 23 levels of branching and over 300 million alveoli in humans The surface area of gas exchange membrane is great relative to its size The thickness of the barrier between the blood and the air is only two layers: the blood vessels and the alveoli Movement of Air Buccal Pressure- used in air breathing fish and amphibians Suction/ Aspiration- used in non-avian reptiles, mammals, and birds, using thoracic and abdominal muscles Tidal Volume- average amount of air taken in a typical breath (500ml) Vital Capacity- maximum amount of air that can be inhaled in a single breath (3.4 – 4.8l) Residual Volume- 1.5l (amount of air left in the lungs after maximum exhalation) Respiratory pigments are needed to bind and transports gases because oxygen has a low solubility in water. Haemoglobin (Fe)- pigment found in erythrocytes that reversible bind to oxygen in vertebrates Haemocyanin (Cu)- pigment in arthropods and most molluscs. Haemoglobin reversibly binds to oxygen molecules, loading oxygen into the lungs and unloading it in other parts of the body with lower partial pressure. 20 Animal Circulatory System Allows exchange with the environment Provides an internal transport system for oxygen, carbon dioxide, nutrients and waste. This system is vital as diffusion is inefficient for internal transport of these substances in larger organisms Three basic components include the circulatory fluid (i.e. blood), a set of tubes (blood vessels) and a muscular pump (heat) Open Circulatory System- blood may be partially or not confined to blood vessels Closed Circulatory System- blood is completely confined to blood vessels. Insects (Open Circulatory System) As the heart relaxes, it draws haemolymph into the system by valved pores called ostia. Earthworms (Closed Circulatory System) Closed systems are more efficient in larger, more active animals. Vertebrate Cardiovascular System Blood Vessels Arteries- carries blood away from the heart to the arterioles to the capillaries. Veins- carries blood from the venules to capillaries and into the heart Capillaries- site of gas exchange Two to four chambered hearts divided into atria and ventricles Fish (Single Circulation) A fish has 2 main chambers- one ventricle and one atrium Blood pressure drops as it flows through the capillary beds. This limits the aerobic metabolic rate of fishes 21 Mammalian Circulatory System Diastole- relaxation phase Systole- contraction phase Factors that influence Cardiac Output- 1. Heart Rate (bpm) 2. Stroke Volume- the amount of blood pumped by the left ventricle (~75ml) The beat is maintained by the sinoatrial and atrioventricular nodes working in unison. Blood Vessels Arteries have thicker, more elastic than veins to help maintain blood pressure between contractions. Slow blood flow in the capillaries allows for the exchange of gases and nutrients. 15% of blood fluids and protein leaks into the lymphatic system and are returned near the right atrium. Muscle movements squeeze blood through the veins 22 Medical Conditions Atherosclerosis- caused by the buildup of LDLs (low density lipoproteins) in the arteries. Hypertension- promotes atherosclerosis and increases the risk of a heart attack/stroke. Heart Attack- the death of cardiac muscle tissue resulting from the blockage of one or more coronary arteries, often caused by a blood clot. Embolus- ruptured plaque Stroke- the death of nervous tissue in the brain, usually resulting from a blockage or rupturing of one of the arteries in the head Blood Blood is a connective tissue that consists of cell (45% by volume) and plasma (90% water & solutes). 23 Animal Digestion There are three dietary categories- herbivores, carnivores, and omnivores Digestion is a necessity in order to provide fuel for all metabolic reactions required by the body, biosynthesis, energy and for essential amino acids which cannot be made by the body. There are 4 stages of digestion- ingestion (mechanical and chemical), digestion (chemical and mechanical), absorption, and egestion/elimination. Chemical digestion involves enzymatic hydrolysis. Digestion can be intracellular i.e. it can happen within the cell like in food vacuoles or it can be extracellular i.e. in a specific compartment of the organism such as hydra have a gastrovascular cavity. Animals avoid self-digestion by processing foods in different compartments. Intracellular Digestion i.e. Endocytosis Extracellular Digestion i.e. Gastrovascular Cavities Digests food and distributes nutrients. Digestion begins in the cavity known as the gastrodermis (secretes enzymes) and is completed intracellularly (engulfed by nutritive muscular cells) Porifera and cnidaria have one opening for the digestive system. Most animals, however, have 2 separate openings for the digestive system = complete digestive tract 24 Human Digestive System Bolus- oral cavity – salivary amylase + mucin + food (1L saliva produced daily) Salivary amylase hydrolyses starch and glycogen Food moves along the oesophagus by peristalsis. When you swallow, the epiglottis opens between the vocal chords From the Mouth to the Stomach 1. When a person is not swallowing, the oesophageal sphincter muscle is contracted, the epiglottis is up, and the glottis is open, allowing air to flow through the trachea to the lungs. 2. The swallowing reflex is triggered when a bolus of food reaches the pharynx. 3. The larynx, the upper part of the respiratory tract, moves upward and tips the epiglottis over the glottis, preventing food from entering the trachea. 4. The oesophageal sphincter relaxes, allowing the bolus to enter the oesophagus. 5. After the food has entered the oesophagus, the larynx moves downward and opens the breathing passage. 6. Waves of muscular contraction (peristalsis) move the bolus down the oesophagus to the stomach. 25 Stomach The interior of the stomach lining is heavily folded to increase its surface area. The gastric gland has three types of cells that secrete different components of the gastric juices Mucus Cells- secretes mucus which lubricates and protects the cells lining the stomach. Chief Cells- secretes pepsinogen, the inactive version of the enzyme pepsin. Parietal Cells- secretes HCl. Pepsinogen and HCl are both secreted into the lumen of the stomach HCl converts pepsinogen to pepsin. Pepsin then causes the chain reaction of pepsinogen conversion to pepsin, inducing protein digestion. Pepsin and HCl can cause ulcers but are prevented by the stomach being lined by mucus. Chyme- partially digested food + gastric juices. Heartburn- the backflow of acidic chyme through the cardiac orifice. Pyloric Sphincter- regulates the passage of chyme into the small intestine. Enzymatic Action in the Small Intestine Duodenum- first part of the small intestine in which the pancreas secretes enzymes. Pancreas The pancreas secretes many enzymes (exocrine function) including protease, amylase, lipase, nuclease and produces sodium bicarbonate The pancreas also has an endocrine function such as the secretion of insulin and glucagon into the bloodstream. Liver The liver produces a substance called bile which consists of bile salts (emulsifiers) and pigments (from the destruction of red blood cells) which is eliminated in faeces. 26 Hormonal Control of the Digestive System Enterogastrone- is secreted by the duodenum, and inhibits peristalsis and acid secretion, slowing down digestion of acid chyme, rich in fat that enters the duodenum. Gastrin- recirculates from the duodenum to the stomach, where it stimulates the production of gastric juices. Cholecystokinin- triggered by amino acids or fatty acids and stimulates the production of digestive enzymes from the pancreas and bile from the gall bladder Large Intestine (Colon) Colon is 1.5 m long Appendix has some defense role Reabsorption of water Rich microflora, mostly harmless, including E. coli. They produce vitamins, which are absorbed by the large intestine Production of faeces Large Intestine (Cecum) Most mammalian herbivores have a relatively large caecum, hosting many bacteria, which aid in the enzymatic breakdown of plant materials such as cellulose; in many species, it is considerably wider than the colon. In contrast, obligatory carnivores, whose diets contain little or no plant material, have a reduced cecum, which is often partially or wholly replaced by the appendix. Microbiome: Current and Future Research 500-1,000 microbial species in the human gut Commensal bacteria convert dietary fibre to short chain fatty acids and vitamin K absorption. Microbiome gut-brain axis research is ongoing. Microbial composition affects anxiety, obesity and memory in mice trials (human trials are still ongoing) The gut microflora is affected by; antibiotics, fermented foods i.e. yoghurt and FMTs (fecal microbia transplants) 27 Plant Hormones Examples of this include seed germination, seed dormancy, fruit/seed development and senescence. Growth- change in size and weight Development- progression in the life cycle. Plant hormones coordinate plant growth and tissue, cells, tissues, and organs Essential for all multicellular organisms Sessile organisms must adjust to environmental change and hormones play a key role in this process Plant Growth Regulators Produced by multicellular organisms Internal, chemical signals Present in minute amounts Travel throughout organism Coordinate metabolic activities Coordinate environmental responses Not produced in glands Hormone Activity at a Cell Level There are 3 steps with components associated with each cell: The first step is reception (receptor), then transduction (signalling cascade) and then cellular response Hormone Reception Specific receptor for each specific hormone Located in the cell membrane Present in extremely low concentrations Identifying a Hormone Response Biochemical purifcation is very difficult Genetic approaches to this topic were deemed successful (based on genetic analysis plant with changes phenotype) 28 Signal Transduction Secondary messengers connect receptors with the response system They transduce and amplify hormone signals Examples include phosphorylation events Cell Response Altered transcription of specific genes (transcriptional regulation) Altered activity enzymes (post-translational regulation) Hormone Metabolism (Environmental Factors Alter) Hormone biosynthesis Hormone transport Hormone conjugation to sugars Hormone perception Hormone degradation Main Classes of Hormones Growth Promoters- i.e. auxin stimulate cell expansion and cytokinin stimulates cell division Growth Inhibitors- i.e. abscisic acid slows growth by dormancy and ethylene controls ripening and cell death Life Cycle (Apical Dominance) Apex block axillary buds from growing (important for competition for light) Auxin is a growth promoter found in the apex and young leaves and is responsible for apical dominance Auxin Also known as indole acetic acid 2,4 D is a form of auxin used as a weed killer (also know as agent orange during the Vietnam War) Mostly produced in shoot apex, young leaves, and embryos. Travels down to roots Blocks axillary buds Promotes the formation of lateral roots Commercially used as rooting powder 29 Cytokinin Most produced in root tips and embryos Most common type is seating Travels up from roots to shoots Promotes cell division Enhances branching axillary buds and growth of such Anti-aging Life Cycle- Auxin and Fruits Fruits are expensive investments Auxin and Gibbberellin produced in embryo stimulate the growth of fruit No embryo means no auxin meaning no fruit produced Flower and young fruit will be shed if there is no viable hormone producing embryo is present. Seedless fruit such as grapes exist This is because they are treated with synthetic auxin or gibberellin, or they could be caused by a genetic mutation Seed Dormancy High levels of giberellic acid promote embryonic growth High levels of abscisic acid facilitate embryo dormancy Cotyledon- embryonic leaf Plumule- first true leaves Hypocotyl- stem below attachment point cotyledons Radicle- embryonic root Initial stage embryo development has high levels of giberellic acid for growth and low levels of abscisic acid In the second stage, it’s the opposite allowing for slower metabolism to occur Dormancy facilitates dispersal and survival. In the third stage, germination occurs as high levels of giberellic acid and low levels of abscisic acid are present The balance of the two hormones determines whether it grows or remains dormant 30 Life Cycle- Fruit Ripening Timing of ripening is carefully regulated Switch from repelling to attracting consumers Softening occurs Sweetening due to conversion of starch to sugars occurs Scent and colour develop Controlled by ethylene Ethylene bursts Ethylene is a gas that stimulates the ripening of fruit with a positive feedback cycle. Ethylene also controls programmed cell death i.e. xylem vessels are dead yet functional Programmed cell death = apoptosis Leaf abscission involves local increases in ethylene and local decreases in auxin Local cell death occurs at abscission layer (shedding) 31 Defence System The gaboon viper (bitis japonica) is both a highly camouflaged and highly venomous snake that is adapted to defend itself. LRS- Lifetime Reproductive Success All forms of life defend themselves from the attack by predators, herbivores, and parasites. Parasites- an organism that lives on or in another organism of another species for at least a part of its life cycle Pathogens- an organism that causes disease to the host after infection Defence can be chemical, biological, and behavioural. LRS is used to track the life of organisms from juvenile to adult and how predators and parasites impact the lives of these organisms. Parasites are much smaller than their host Parasites Parasites have a shorter life expectancy than their host Parasites infect one or a few host Rarely kills the host They have both macro and micro forms Definitions are in part based on immune response Predators Predators are much larger than their host They have a larger life expectancy than their host They attack many different preys in their lifetime Always kills their prey Insect predators (parasitoids) always kill their host or prey Mosquito Also known as aedes aegypti It is a vector of numerous diseases such as yellow fever They are intermittent ectoparasites (proboscis) They transmit malaria which kills 0.5 million people every year Micropathogens aka Mircoparasites Small in size Replicate very quickly Undergo direct replication in the host Easily transmitted directly Can cause severe mortality and morbidity Adaptive immune response is robust and long lasting They include viruses, bacteria, and protozoa. 32 Macroparasites Large in size Do not reproduce quickly Generally, do not replicate directly in host Not transmitted directly Complex life cycles often with at least two intermediate hosts Generally, do not cause morbidity to the host and mass mortality is rare Morbidity is related to the amount of macroparasites present (dose dependent) Immune response is weak and short lived Examples include ticks, tapeworm, and fleas Points to Note Both attack and defence can be expensive in terms of energy allocation Defence can be used in attack and vice versa Benefits must outweigh the cost Basic Defences in Bacteria Bacteria have an immune defence Recently discovered CRISPR CAS 9 CAS 9 is an enzyme which acts by cutting out part of the invading viral nucleic acid This helps bacteria act against phages Basic Defences in Animals Structural defence includes spikes, quills, horns, and modified skin Skunks have foul odour Salamanders have poison Fulmar petrels have foul oily projectile regurgitates Basic Defences in Plants Immobile organisms and are attacked by herbivores Most are insects and the interaction dominates the terrrastrial ecology of the Earth. Above ground and below ground attacks The two broad types of defence include constitutive and inductive Constitutive- preformed, permenantly present (physical and chemical) Inductive- induced attack by volatile organic compounds (VOC) and BVOC Primarily chemical Very complex Allelopathic Secondary metabolite based Insects are attracted so conflicting signals are provided by the plant 33 Constitutive Compounds Introduce well known alkaloids such as nicotene and cocaine. All which have a negative affect on insect grazers Many other compounds have a similar effect All are inprotant in insect herbivore population dynamics Inductive Compounds BVOC- biochemical volatile organic compounds HIPV- herbivore induced plant volatiles Allelopathic- chemicals released by one organism that affects the growth and reproduction in another Secondary metabolites Summon natural enemies of insect herbivores Exert effect on nearby plants Controversial topic Poisons Compounds that are produced or sequester by animals One such animals is the cane toad which produces bufotoxin from the eye gland Poisonous to predators Must be consumed or in rare cases sprayed into eyes or exposed skin Pufferfish also have skin which is highly toxic Venoms Toxic substance introduced by a bit (needs mechanical damage to work) Result is often fatal Sometimes it is exclusively defensive such as bees and wasps It can also be both defensive and offensive such as in snakes Convergent evolution in chemical structure and toxic action 34 Snake Venoms Only 300 of 2000 snake species are venomous (mild venoms in others) At least 1,000,000 snake bites per year? At least 100,000 fatal Venomous families are: Colubridae (Boomslang). Elapidae; Cobra, Mamba, Taipan, Coral Snake. Hydrophidae (Sea Snakes). Viperidae (Puff Adders) Crotalidae: Pit Vipers Venoms primarily attack but also defence (Rattle snake) 95% of dry weight is Protein -polypeptide (so, proteins and peptides) Long and short chain Some species have both Nonvenomous bites as well; but fatal bites may not show ill effects for 10+hours Neuro-toxic and haemorrhagic (but also cytotoxic and myotoxic). Aposematic Colouration Warning colouration Usually red and yellow, yellow and black, or orange and red Blue and green with black stripes in rare cases is also indicative of venomous organisms Indicates unpalatability Universal code ensuring safety Mimicry 1) Mullerian Mimicry = Imitative similarity – typically based on warning colouration – amongst a number of mimic species all of which are unpalatable or otherwise offensive to a predator. 2) Batesian: Close resemblance of palatable i.e. harmless species (the mimic) to an unpalatable or poisonous/venomous species (the model) to deceive the predator (Operator) Complex and controversial subject Overlap between the two types Overall is an important evolutionary strategy Both forms confer adaptive advantages Sometimes difficult to see due to camoflauge 35 Camouflage and Crypsjs Widely seen in nature Both defensive and offensive Some overlap with the Bayesian mimicry and mimicry in general Peppered Moth Biston bitularia-Famous controversy 36 Endocrine System During an animal’s life cycle a lot of decisions have to be made but how do they know which decision is the best in order to survive They decisions affect both population size, structure, and the evolution of species as a whole. Animals respond to stimuli such as environmental, behavioural, and physiological cues. Overall, anything that requires energy must be chosen using decisions that make an organism as energy efficient as possible. The first discovery of this decision making was discovered by Bayliss and Starling in 1902, when they discovered secretion of hormones into the duodenum by the pancreas. Hormones by their signalling system are able to control many aspects of life Hormones are chemical messengers that transmit widespread signals around the body by specific glands and transpire information from one set of cells to another by the bloodstream. Hormones help the body to maintain homeostasis. The function of the endocrine system is the production and regulation of chemical substances called hormones Not all signaling molecules act within the body such as pheromones in bees, moths, and ants i.e. Polyphemus giant silk moth Classes of Hormones There are three major classes which are polypeptides (water soluble) such as insulin, amines (water soluble) such as thyroxine and steroids (lipid soluble) such as cortisol. Water soluble hormones cannot diffuse through the plasma membranes of target cells. Instead, they bind to cell surface receptors then induce changes in cytoplasmic molecules and sometimes alter gene transcription. Lipid soluble hormones diffuse out across the membrane of endocrine cells where they bind to transport proteins in the blood then diffuse into the target cells and bind to receptors in the cytoplasm or nucleus and trigger changes in gene transcription. Some hormones can induce multiple effects such as adrenaline. This hormone can cause glucose blood levels to rise in the liver, causes blood vessels to dialate in smooth muscle cells that supplies the skeletal muscle and constricts blood vessels in smooth muscle cells that supplies the intestine 37 Why are Endocrine Cells in the Body? Grouped in ductless organs called endocrine glands- secrete hormones directly in fluids in the body Exocrine systems have glands i.e. salivary glands Hormones are also made in other organs in the body i.e. the brain Neuroendocrine The nervous system and endocrine help maintain homeostasis in the body The hypothalamus is a collection of specialised cells located in the brain and is the primary link between the two systems. It produces chemicals that either stimulate or suppress the hormone secretions of the pituitary gland. How is Hormone Secretion Controlled? They are controlled by both positive and negative feedback systems Negative Feedback System- the endocrine cells respond to an internal or environmental stimulus by secreting a hormone. The hormone travels to the target cell, where it interacts with the specific receptor to bring about a physiological response. Positive Feedback System- where continued stimulation causes an increase of the hormone i.e. oxytocin Positive feedback amplifies both the stimulus and response Negative feedback helps to restore to a pre-existing state. Hormone pathways involved in homeostasis involve negative feedback. Co-Ordination of Endocrine and Nervous System Invertebrates Ecdysis Giant silk moth Hyalophora cercopia PTTH Ecdysteroid Moult or Metamorphosis Juvenile hormone Insect growth regulators 38 Vertebrates Hypothalamus Pituitary gland Posterior pituitary – extension of hypothalamus Anterior pituitary- releasing or inhibiting hormones i.e. prolactin releasing hormone Antidiuretic hormone (ADH) Oxytocin Hormones have a cascading pathway The path goes from hypothalamus > anterior pituitary > target endocrine gland > target tissue What stimulates endocrine glands to secrete hormones? Blood concentrations of non-hormone chemicals e.g. ADH Another hormone Neural stimuli e.g. noradrenaline and adrenalin Evolution of Hormone Function Same hormones – distinct functions e.g. Prolactin Mammals – growth of mammary glands and milk production Birds – regulates fat metabolism, reproduction (parental care) Amphibians – delays metamorphosis FW fish – regulates salt and water balance 39 Reproductive System Asexual reproduction- requires one parent organism Sexual reproduction- requires two parent organisms and the fusions of male and female gametes to form a zygote Mechanisms of Asexual Reproduction Many invertebrates reproduce asexually by fission Fission- separation of a parent into two or more individuals of approximately the same size Budding, fragmentation and parthenogenesis (a process in which an egg develops without being fertilised) are also extremely common in invertebrates Sexual Reproduction Two parents each with their own reproductive organs to produce gamete’s Testes in the male produce sperm Ovaries in the female produce ova (eggs) Reproductive Strategies Internal vs External fertilisation Semelparity- single reproductive episode before death i.e. octopus, salmon, etc… Iteroparity- multiple reproductive episodes over life span External Fertilisation- eggs shed by the female are fertilised by the sperm in an external environment Internal Fertilisation- sperm are deposited in or near the female reproductive tract, and fertilisation occurs within the tract. Reproductive Cycles Most animals exhibit cycles on reproductive activity It is often related to changing seasons Reproductive cycles are controlled by hormones and environmental cues Hermaphroditism & Alternation of Sexes Simultaneous Hermaphroditism- self fertilisation with both gametes present Sequential Hermaphroditism (Protandrous)- male first Sequential Hermaphroditism (Protogynous)- female first 40 Female Gametes Oviparity- eggs laid outside the body Ovoviviparity- eggs hatch in mother’s uterus and nutrients are stored in the egg Viviparity- no eggs but instead the embryo develops inside the mother. This occurs in all mammals except monotremes Insects Reproductive System Have separate sexes with complex reproductive systems The male honeybees which have sperm that forms in the testes, which then passes through the sperm ducts and are stored in the seminal vesicles. The male ejaculates sperm along with fluid from the accessory gland Males of some species of insects and other arthropods have appendages called claspers gang grasp the female during copulation The female honeybee has eggs which develop on the ovaries, which then pass though the oviducts and into the vagina A pair of accessory glands add protective secretions to the eggs in the vagina. After mating sperm are stored in the spermatheca, a sac connected to the vagina by a short duct. Mammalian Male Reproductive Sytem Testes- consist mainly of highly coiled tubes surrounded by several layers of connective tissue Seminiferous Tubules- where sperm form From the seminiferous tubules of a testis, the sperm can pass into the coiled tubules of the epididymis. During ejaculation, sperm is propelled through the muscular sperm ducts, the ejacuatory duct, and exit the penis through the urethra Spermatogenesis- male meiosis forming sperm Accessory Glands There are three sets of accessory glands in the male reproductive systems pair of seminal vesicles contribute to 60% of the total volume of semen Prostate gland- secretes its products directly into the urethra through several small ducts. Semen- consists of sperm cells plus fructose and other energy source for sperm and acid-base buffers that create a suitable environment for the sperm Testosterone- sperm production, secondary sex characteristics and sex drive Mammalian Female Reproductive System The ovaries lie in the abdominal cavity 41  Each ovary is enclosed in a tough, protective capsule and contain many follicles Follicle- consists of one egg cell surroinddd by one or more layers of follicle cells Ovulation- expels an egg cell from the follicle The remaining follicular tissue then grows within the ovary to form a solid mass called the corpus luteum, which secretes hormones depending on whether or not pregnancy occurs Oogenesis- female meiosis forming ova Oogenesis In foetal ovaries, diploid oogonia divide by mitosis to produce many more oogonia All oogonia undergo the first stage of meiosis during foetal life or shortly afterward, being called primary oocytes Primary oocytes remain as such until they are ovulated Primary oocytes completes the meiotic division at ovulation The second meiotic division is completed only of the oocyte is ovulated Tissue Hormone Class Function Ovary Estrogen Steroid Involved on ovulation and pregnancy Ovary Progesterone Steroid Prepared uterus for pregnancy Oviducts and the Uterus The egg cell is released into the abdominal cavity, near the opening of the oviduct or fallopian tube Cilia in the tube convey the egg to the uterus 42 Ovarian Cycle Luteal Phase Corpus Luteum- cells of the ruptured nature follicle form this structure Luteinising hormone after ovulation initiates the transformation of the corpus luteum If the oocyte in the oviduct is not fertilised, the corpus luteum degenerates. If fertilisation occurs, the corpus luteum grows and continues to secrete hormones, mainly progesterone and estrogens. Estrogens is secreted by the follicles and corpus luteum stimulates the growth of the endometrium of the uterus and the production of progesterone receptors in the endometrium The corpus luteum is essential for establishing conditions that permit implantation and pregnancy Fertilisation Acrosome Reaction- membrane fusions activate the egg When sperm makes contact with the egg’s plasma membrane, it triggers the release of calcium from internal organelles starting at the point of sperm entry. This changes the membrane potential of egg, preventing other sperm from fusing with the egg. Prevents polyspermy 43 Nervous System All bodily systems are integrated into each other An example of this is barnacles which use their strand like structures to filter feed (digestion), respire (respiration) and excrete (excretion). Other marine organisms such as sponges, which have specialised cells such porocytes to help absorb water and excrete any unnecessary waste. Command & Control Controls feelings, perceptions and movements Enables us to learn, think remember and be conscious of ourselves and our surroundings Regulates internal bodily functions and behaviours Lines of Communication There are three main functions: sensory input, integration, and motor output Sensory detects stimuli and internal conditions and transmit information along sensory neurons Sensory information is sent to the brain or ganglia, where interneurons integrate/process the information. Occurs in the CNS. Motor outputs leave the brain/ganglia via motor neurons which trigger muscle/gland activity Neurons- nerve cells that transfer information within the body The transmission of information depends on the path of neurons on which a signal travels Processing of information takes place in a simple cluster of neurons known as the ganglia or a more complex structure known as the brain Neurons Their function is to transmit signals Most neurons have dendrites (GK tree), highly branched extensions that receive signals from other neurons The axon is typically a much longer extension that transmits signals from its terminal branches to other cells at synapses Most of a neuron's organelles are in the cell body Most neurons are nourished/insulated by cells called glia Every cell has a voltage (difference in electrical charge in its plasma membrane called a membrane potential) 44  Messages travel along as there is changes in membrane potential The resting potential is the membrane potential when a neuron is not sending signals Ion pumps & channels maintain the resting potential of a neuron Neuron - Formation of the Resting Potential At resting potential, the concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell. Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane. These concentration gradients represent chemical potential energy. The opening of ion channels in the plasma membrane converts chemical potential to electrical potential. A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell. Anions trapped inside the cell contribute to the negative charge inside the neuron. In a resting neuron, the currents of K+ and Na+ are equal and opposite, and the resting potential across the membrane remains steady. Formation of Action Potentials During the refractory period after an action potential initiates, a second action potential cannot be initiated. This ensures that an impulse moves along the axon in one direction only. The refractory period is a result of a temporary inactivation of the Na+ channels. The refractory period is a period of “normal” repolarization when the Na+ K+ pump restores the membrane to its original polarized condition. i.e. resting stage and cycle begins again 45 Conduction of Action Potentials An action potential can travel long distances by regenerating itself along the axon. At the site where the action potential is generated, an electrical current depolarizes the neighbouring region of the axon membrane. Inactivated Na+ channels behind the zone of depolarization prevent the action potential from traveling backwards. Action potentials travel in only one direction: toward the synaptic terminals The speed of an action potential increases with the axon’s diameter. In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase. Myelin sheaths are made by glia— oligodendrocytes in the CNS and Schwann cells in the PNS. Action potentials are formed only at nodes of Ranvier, gaps between Schwann cells in the myelin sheath where voltage-gated Na+ channels are found. Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction. Neurons communicate with other cells at synapses Synapse- a junction between cells controlling communication At electrical synapses, the electrical current flows from one neuron to another. At chemical synapses, a chemical neurotransmitter carries information across the synapse. Most synapses are chemical synapses. There are two types of synapses - The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters. - Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell). 46 Chemical synapses The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal. The action potential causes the release of the neurotransmitter. The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell. Direct synaptic transmission involves binding of neurotransmitters to ligand- gated ion channels in the postsynaptic cell. Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential. After release, the neurotransmitter - May diffuse out of the synaptic cleft - May be taken up by surrounding cells - May be degraded by enzymes Nervous systems consist of circuits of neurons and supporting cells The simplest animals with nervous systems, the cnidarians, have neurons arranged in nerve nets. A nerve net is a series of interconnected nerve cells. There is no central pathway/directional organization. Starfish - a nerve net in each arm Connected by radial nerves to a central nerve ring Bilaterally symmetrical animals exhibit cephalization. Cephalization- the clustering of sensory organs at the front end of the body. Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS). The CNS consists of a brain and longitudinal nerve In Vertebrates 47  A central nervous system (CNS) composed of the brain and spinal cord. Here integration of information takes place. A peripheral nervous system (PNS) composed of nerves and ganglia, which brings information into and out of the CNS. Central Nervous System The brain and spinal cord contain: - Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons. - White matter, which consists of bundles of myelinated axons Organization of the Vertebrate Nervous System A reflex is the body’s automatic response to a stimulus. For example, a doctor uses a mallet to trigger a knee-jerk reflex. Peripheral Nervous System The PNS transmits information to and from the CNS and regulates movement and the internal environment. In the PNS, afferent neurons transmit information to the CNS and efferent neurons transmit information away from the CNS. Cranial nerves originate in the brain and mostly terminate in organs of the head and upper body. Spinal nerves originate in the spinal cord and extend to parts of the body below the head. The PNS has two functional components: the motor system and the autonomic nervous system. The motor system carries signals to skeletal muscles and is voluntary. The autonomic nervous system regulates the internal environment in an involuntary manner. The Brain The vertebrate brain is regionally specialized Brainstem- coordinates and conducts information between brain centres. The brainstem has three parts: the midbrain, the pons, and the medulla oblongata. Midbrain- contains centres for receipt and integration of sensory information. Pons- regulates breathing centres in the medulla 48 Medulla Oblongata- contains centres that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion. The cerebellum is important for coordination and error checking during motor, perceptual, and cognitive functions. It is also involved in learning and remembering motor skills.eg hand-eye coordination The embryonic diencephalon develops into three regions: - The epithalamus includes the pineal gland and generates cerebrospinal fluid from blood. - The thalamus is the main input centre for sensory information to the cerebrum and the main output centre for motor information leaving the cerebrum. - The hypothalamus regulates homeostasis and basic survival behaviours such as feeding, fighting, fleeing, and reproducing. Cerebrum The cerebrum has right and left cerebral hemispheres. Each cerebral hemisphere consists of a cerebral cortex (gray matter) overlying white matter and basal nuclei. In humans, the cerebral cortex is the largest and most complex part of the brain. A thick band of axons called the corpus callosum provides communication between the right and left cerebral cortices. The right half of the cerebral cortex controls the left side of the body, and vice versa. The cerebral cortex controls voluntary movement and cognitive functions Each side of the cerebral cortex has four lobes: frontal, temporal, occipital, and parietal. Each lobe contains primary sensory areas and association areas where information is integrated. The Limbic System Emotions are generated and experienced by the limbic system and other parts of the brain including the sensory areas. The limbic system is a ring of structures around the brainstem that includes the amygdala, hippocampus, and parts of the thalamus. The amygdala is in the temporal lobe and helps store an emotional experience as an emotional memory. 49 Memory and Learning Learning can occur when neurons make new connections or when the strength of existing neural connections changes. Short-term memory is accessed via the hippocampus. The hippocampus also plays a role in forming long- term memory, which is stored in the cerebral cortex. Excretion Overview: A Balancing Act Physiological systems of animals operate in a fluid environment. Relative concentrations of water and solutes must be maintained within fairly narrow limits. Osmoregulation regulates solute concentrations and balances the gain and loss of water. Freshwater animals show adaptations that reduce water uptake and conserve solutes. Desert and marine animals face desiccating environments that can quickly deplete body water. Excretion gets rid of nitrogenous metabolites and other waste products. Osmoregulation balances the uptake and loss of water and solutes Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment. Cells require a balance between osmotic gain and loss of water. Osmosis = movement of water across a selective permeable membrane Osmolarity = the solute concentration of a solution, determines the movement of water across a selectively permeable membrane. If two solutions are isosmotic, the movement of water is equal in both directions. 50  If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution. Osmotic Challenges Osmoconformers, consisting only of some marine animals, are isosmotic with their surroundings and do not regulate their osmolarity. Most marine invertebrates are osmoconformers. Stenohaline (narrow) vs Euryhaline (wide) tolerances in osmoconformers & regulators Osmotic Challenges Osmoregulators expend energy to control water uptake in a hypoosmotic environment and loss in a hyperosmotic environment. Marine bony fishes are hypoosmotic to sea water. They lose water by osmosis and gain salt by diffusion and from food. They balance water loss by drinking seawater and excreting salts. Osmoregulators expend energy to control water uptake in a hypoosmotic environment and loss in a hyperosmotic environment. Marine bony fishes are hypoosmotic to sea water. They lose water by osmosis and gain salt by diffusion and from food. They balance water loss by drinking seawater and excreting salts. Osmoregulators expend energy to control water uptake in a hypoosmotic environment and loss in a hyperosmotic environment. Freshwater animals constantly take in water by osmosis from their hypoosmotic environment. They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine. Salts lost by diffusion are replaced in foods and by uptake across the gills. 51 Animals That Live in Temporary Waters Some aquatic invertebrates in temporary ponds lose almost all of their body water and survive in a dormant state. This adaptation is called anhydrobiosis. Land Animals Land animals manage water budgets by drinking and eating moist foods and using metabolic water. Desert animals get major water savings from simple anatomical features and behaviours such as a nocturnal lifestyle / underground existence. Energetics of Osmoregulation Osmoregulators must expend energy to maintain osmotic gradients. Animals regulate the composition of body fluid that bathes their cells. Transport epithelia are specialized epithelial cells that regulate solute movement. They are essential components of osmotic regulation and metabolic waste disposal. They are arranged in complex tubular networks An animal’s nitrogenous wastes reflect its phylogeny and habitat The type and quantity of an animal’s waste products may greatly affect its water balance. Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids. The type and quantity of an animal’s waste products may greatly affect its water balance. Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids. Nitrogenous wastes Ammonia – toxic - needs lots of water. Common in aquatic species. Urea - The liver of mammals and most adult amphibians converts ammonia to less toxic urea. The circulatory system carries urea to kidneys, where it is excreted. 52  Conversion of ammonia to urea is energetically expensive; less water is required to excrete. Many reptiles (including birds), insects, land snails Uric Acid - Insects, land snails, and many reptiles, including birds, mainly excrete uric acid. Uric acid is largely insoluble in water; can be secreted as a paste with little water loss. Uric acid is more energetically expensive to produce than urea. Diverse excretory systems are variations on a tubular theme Excretory systems regulate solute movement between internal fluids and the external environment. Most excretory systems produce urine by refining a filtrate derived from body fluids. Key functions of most excretory systems: Filtration: pressure-filtering of body fluids Reabsorption: reclaiming valuable solutes Secretion: adding toxins and other solutes from the body fluids to the filtrate Excretion: removing the filtrate from the system. Excretory Systems Systems that perform basic excretory functions vary widely among animal groups. They usually involve a complex network of tubules. Protonephridia flame cells / planaria Metanephridia earthworm / like nephrons Malpighian Tubules insects Nephrons = the function unit of the kidneys / humans. Protonephridia- protonephridium is a network of dead-end tubules connected to external openings. The smallest branches of the network are capped by a cellular unit called a flame bulb. These tubules excrete a dilute fluid and functionin osmoregulation. 53 Metanephridia Each segment of an earthworm has a pair of open-ended metanephridia. Both excretory and osmoregulatory functions Metanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretion. Malpighian Tubules In insects and other terrestrial arthropods, malpighian tubules remove nitrogenous wastes from hemolymph and function in osmoregulation. MT open into digestive tract. Insects produce a relatively dry waste matter, an important adaptation to terrestrial life. Highly efficient in water conservation Kidneys Kidneys- excretory organs of vertebrates, function in both excretion and osmoregulation. Mammalian excretory systems center on paired kidneys, which are also the principal site of water balance and salt regulation. Each kidney is supplied with blood by a renal artery and drained by a renal vein. Urine exits each kidney through a duct called the ureter. Both ureters drain into a common urinary bladder, and urine is expelled through a urethra. Nephrons = the Functional Unit The nephron = the functional unit of the vertebrate kidney, consists of a single long tubule and a ball of capillaries called the glomerulus. Bowman’s capsule surrounds and receives filtrate from the glomerulus capillaries. Filtration: Glomerulus --> Bowman’s Capsule Filtration occurs as blood pressure = hydrostatic pressure forces fluid from the blood in the glomerulus to lumen of Bowman’s capsule. Filtration of small molecules is nonselective. 54  The filtrate contains salts, glucose, amino acids, vitamins, nitrogenous wastes, and other small molecules Pathway of the Filtrate From Bowman’s capsule, the filtrate passes through three regions of the nephron: the proximal tubule --> loop of Henle --> distal tubule... Fluid from several nephrons flows into a collecting duct ---> renal pelvis ---> ureter. Vasa recta are capillaries that serve the loop of Henle. The vasa recta and the loop of Henle function as a countercurrent system. The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids. The mammalian kidney conserves water by producing urine that is much more concentrated than body fluids. The nephron is organized for stepwise processing of blood filtrate Proximal Tubule Reabsorption of ions, water, and nutrients takes place in the proximal tubule. Molecules are transported actively and passively from the filtrate into the interstitial fluid and then capillaries. Some toxic materials are secreted into the filtrate. The filtrate volume decreases. Descending Limb of the Loop of Henle Reabsorption of water continues through channels formed by aquaporin proteins. Movement is driven by the high osmolarity of the interstitial fluid, which is hyperosmotic to the filtrate. The filtrate becomes increasingly concentrated. Ascending Limb of the Loop of Henle In the ascending limb of the loop of Henle, salt but not water is able to diffuse from the tubule into the interstitial fluid. The filtrate becomes increasingly dilute. Distal Tubule 55  The distal tubule regulates the K+ and NaCl concentrations of body fluids. Collecting Duct The collecting duct carries filtrate through the medulla to the renal pelvis. Water is lost as well as some salt and urea, and the filtrate becomes more concentrated. Urine is hyperosmotic to body fluids. Human kidneys process approximately 180 litters of filtrate per day 99% of water and nearly all sugars, amino acids, vitamins, are reabsorbed. Adaptations of the Vertebrate Kidney to Diverse Environments The form and function of nephrons in various vertebrate classes are related to requirements for osmoregulation in the animal’s habitat. The juxtamedullary nephron contributes to water conservation in terrestrial animals. Mammals that inhabit dry environments have long loops of Henle, while those in fresh water have relatively short loops. Birds and Other Reptiles Birds have shorter loops of Henle but conserve water by excreting uric acid instead of urea. Other reptiles have only cortical nephrons but also excrete nitrogenous waste as uric acid. 56