Grade 8 Study Guide Semester 2.pptx

Stimulus & Response Stimuli ⚫Stimuli are changes that occur around us in the environment. ⚫Stimuli is known to us as touch, pain, heat, cold, sounds, food (chemicals) and light. ⚫For example: - You feel and touch objects - You look at things around you - You feel cold or hot - You feel pain when...

Stimulus & Response Stimuli ⚫Stimuli are changes that occur around us in the environment. ⚫Stimuli is known to us as touch, pain, heat, cold, sounds, food (chemicals) and light. ⚫For example: - You feel and touch objects - You look at things around you - You feel cold or hot - You feel pain when you fall down - You hear sound - You taste a burger Stimulus & Response ⚫Stimulus means a lot of stimuli (or plural form of stimuli). ⚫When a stimuli or stimulus come to us, we respond to it or them. ⚫For every stimuli there is a response to it whether we aware or not. Eg; when we touch anything hot like an iron, we will feel pain and the response would be pulling back the hand to avoid pain. ⚫Human need to respond to stimuli in order to protect themselves from danger or for survival. So.... ⚫The change in the environment is the stimulus; the reaction of the organism to it is the response. Detecting Stimuli ⚫Living objects have sensors (or senses) that detect forms of energy from the world around them. They then convert the energy into a signal. ⚫Human senses include the sense of sight, hearing, smell, taste and touch. ⚫The signal from a sensor may be quite simple or very complex, as in the case of information on images detected by the eye. Signal Interpretation ⚫An organism will process or interpret the signal from the sensor, resulting in a response or being ignored. ⚫The signal may be processed near the sensor, in the brain, or in an area in between. ⚫Plants and lower level animals don't have brains – so deal with this differently. Signal Interpretation Processed before the brain: ⚫ Eg; the skin can detect heat. If the heat is interpreted as dangerously high, the person will jerk away from the source of heat. ⚫ The signal does not have to reach the brain for the interpretation to cause the response in this situation. Processed in brain: ⚫ Eg; the nose of a dog senses the odour from food being offered. The signal reaches the brain which interprets the smell as something good to eat. The dog then responds by salivating. ⚫ This response is its behaviour to the stimulus. Signal Interpretation ⚫On a more complex level, a person may hear a song on the radio. The song is sensed and processed, and its words are interpreted for their meaning. ⚫This goes well beyond responding to a loud noise. The words and melody are presented as complex information, and their interpretation can result in an emotional response or behaviour. Types of Responses ⚫The response to a stimulus can be positive, negative, or ignored as not important. ⚫A positive reaction means that the being wants more or is attracted to the stimulus. ⚫A negative reaction means that the being wants to avoid the stimulus. Examples of Types of Responses Positive ⚫ A plant grows toward sunlight. ⚫ A person laughs after hearing a funny joke. Negative ⚫ The roots of a plant avoid a piece of copper in the ground. ⚫ You make a face or cover your nose after smelling a pungent unpleasant odour. Ignored ⚫ A dog pays no attention to sounds from the television. ⚫ You pay no attention to slight changes in the room's temperature. Homeostasis ⚫Homeostasis is the term we use to describe the constant state of the internal environment. ⚫The cells in your body work best when their surroundings are kept constant. ⚫Your body has many mechanisms that keep the cells surroundings constant even though your external environment is changing. This is homeostasis. ⚫Homeostasis is very important because when it fails you could become ill or may even result in death. CNS & PNS WHAT IS THE NERVOUS SYSTEM MADE UP OF? The nervous system is separated into 2 parts: ⚫ The Central Nervous System (CNS) ⚫ Then Peripheral Nervous System (PNS) CENTRAL NERVOUS SYSTEM (CNS) The Central Nervous System consists of the brain and spinal cord. It contains millions of neurones (nerve cells). In humans, the right side of the brain controls the left side of the body, whilst the left side of the brain controls the right side of the body THE ENDOCRINE SYSTEM WHAT IS THE ENDOCRINE SYSTEM? The function of the endocrine system is the production and regulation of chemical substances called hormones. The endocrine system regulates all biological processes in the body from conception through adulthood and into old age WHAT MAKES UP THE ENDOCRINE SYSTEM? GLANDS AND HORMONES ENDOCRINE GLANDS The primary endocrine glands are the pituitary (the master gland), pineal, thyroid, parathyroid, adrenals, ovaries in the female and testes in the male. HORMONES….. A hormone is a chemical transmitter. It is released in small amounts from glands, and is transported in the bloodstream to target organs or other cells. Hormones are chemical messengers, transferring information and instructions from one set of HORMONES…. regulate growth and development, mood, tissue function, metabolism, and sexual function. HORMONES…. Hormones act slower than nervous impulses but cause longer-lasting effects Hormones are used to stabilize the body’s internal environment (homeostasis) HORMONES…. The endocrine system and nervous system work together to help maintain homeostasis…Balance The hypothalamus in the brain is the primary link between the two systems. It produces chemicals that either stimulate or suppress hormone secretions of the pituitary gland. HOW COMMUNICATION HAPPENS? Hormones follow a complex path to reach their target. Generally a releasing hormone is released from the hypothalamus. This releasing hormone acts on cells in the pituitary gland to release a stimulating hormone which then acts on the endocrine gland or organ. If there is a break anywhere in the path it can cause disorder or disease. PITUITARY GLAND THYROID Produces the hormone thyroxine: Regulates rate of metabolism. Excess causes hyperactivity. Deficiency causes weight gain and sluggishness. ADRENAL GLAND ‘FIGHT’ OR ‘FLIGHT’ The "fight or flight response" is our body's primitive, automatic, inborn response that prepares the body to "fight" or "flee" from perceived attack, harm or threat to our survival. ‘FIGHT’ OR ‘FLIGHT’ The release of adrenaline and norepinephrine from the adrenal glands to the respiratory centres, heart, and blood vessels is triggered by the production and release of the hormone acetylcholine from the nerves. These hormones are responsible for the constriction of blood vessels, the increase in breathing and the heart rate, the tightening of muscles. They work during times of real or perceived danger. PANCREAS Produces the hormone glucagon: Converts of glycogen back to glucose in the liver. Produces the hormone insulin: Controls the conversion of blood glucose to glycogen, which is stored in the liver. REPRODUCTIVE ORGANS REPRODUCTIVE ORGANS Cells Cells Cells are the basis of life Living organisms range from single celled organism (unicellular) to complex organisms (multicellular) Cell theory 1. All living things are composed of one or more cells 2. The cell is the smallest entity that retains the properties of life 3. All cells come from pre-existing cells. Structure of cells Living things are classified into different kingdoms based on the characteristics of their cells. Plants and animals have specific types of cells with similarities and differences. Plant and animal cells contain membrane bound organelles, these are tiny structures that carry out specific functions within the cell. Plant cell structure Animal Cell Structure Plant V Animal Cell Connective Tissue Function - Support - Binds other tissues together - Protects against damage, infection and heat loss Examples: Fat, bone, cartilage, ligaments and tendons Muscle Tissue Function Can contract when stimulated by nerve impulses. Key structural feature Made of long and thin thread like cells called muscle fibres. ADAPTATIONS AND EVOLUTION ADAPTATIONS ⦿ Organisms that are native to a particular environment, have developed adaptations that enable them to survive and breed successfully. ⦿ These adaptations are inherited from parent to offspring and come about as a result of genetic mutations and natural selection. ⦿ All organisms including plants have adaptations. ⦿ There are three main types of adaptations; ◼Structural ◼Functional STRUCTURAL ADAPTATIONS These are physical features of an organism ⦿Examples include ◼Camouflage – to help organisms blend into their surroundings making them less visible to predators. Can you spot me? STRUCTURAL ADAPTATIONS ⦿ Insulation: ◼E.g. layers of fat or fur ◼To keep animals warm in colder climates. STRUCTURAL ADAPTATIONS ◼Size – smaller animals are more suited to very hot climates and larger organisms are better suited to cooler environments. FUNCTIONAL ADAPTATIONS ⦿ Affect how the internal functions of an organism works. ⦿ Examples include: ◼Sweating - helps animals cool down so they don’t overheat. ◼Shivering when cold - helps to warm the body. ◼Animals can hibernate (reduction in metabolism) in winter when food is scarce. ◼Organisms such as the chameleon lizard can change colour to blend in with its environment. BEHAVIOURAL ADAPTATIONS ⦿ Involve the way in which animals act to help them survive in their environment. ⦿ Examples include: ◼Behaviour to avoid predators, such as Freezing when predators come near Living in larger groups / herds ◼Activity patterns which help them avoid unfavorable conditions: Diurnal – active during the day Nocturnal – active at night Crepuscular – active at dawn and dusk VARIATION ⦿ Describes the differences seen within species. ⦿ Variation comes from: ◼The differences in genes and chromosomes that individuals inherit from their parents. ◼Mutations ◼Environmental factors such as diet and habitat ⦿ These variations can either help or hinder an organism within its environment. ◼E.g. people with light skin living in hot climates like Australia are more prone to developing skin cancer than those with dark FAVOURABLE CHARACTERISTICS ⦿ These are characteristics that help organisms survive and successfully reproduce within their environment. ⦿ Through successful reproduction, these characteristics are passed on, becoming the most common. ⦿ Organisms with unfavorable characteristics are unsuited to their environment are more likely to die off, becoming less common. ⦿ This is known as natural selection DARWIN’S THEORY ⦿ Charles Darwin was a naturalist who traveled extensively, observing the geographical distribution of plants, animals, fossils and rocks in various parts of the world. ⦿ Believed in natural selection ◼Variations in characteristics appear within a species ◼nature picked the favourable characteristics over many generations. ◼Less favourable characteristics died out. ◼Survival of the fittest Charles Darwin (18091882) DARWIN’S GIRAFFES Ancestral giraffes had necks of different lengths By natural selection those with longer necks survived and produced long necked offspring Eventually all giraffes had long necks TYPES OF EVOLUTION Divergent evolution ⦿ new forms evolving from a single ancestor ⦿ Results in phenomena known as adaptive radiation HOMOLOGOUS STRUCTURES ⦿ In related species, characteristics have the same basic structure are called homologous characteristics. ⦿ This is because related organisms share some of their genes. ⦿ Studies of vertebrates show that they all have what is known as a pentadactyl limb (a limb with 5 digits) ⦿ Different animals have adapted these to perform different functions. CONVERGENT EVOLUTION ⦿ Organisms from quite different origins evolve similar adaptations. ⦿ They can have analogous structures- body parts that appear to be similar ⦿ E.g. sharks (cartilagenous fish) and dolphins (mammals) are different species however they have similar adaptations that enable them to move through water quickly. PARALLEL EVOLUTION ⦿ Organisms that look alike and have common ancestry, but are found in different locations Inheritance Relationship between genes and traits As chromosomes exist in pairs, sexually reproducing organisms, including humans, have two copies of each gene which code for a particular trait These two copies can be the same -> Homozygous Or they can be different -> Heterozygous Different versions of the same gene are known as alleles. Eg. There are 2 versions of the colour gene for peas, yellow and green. Dominant alleles In general, alleles can be thought of as either dominant or recessive. A dominant allele produces an observable phenotype in individuals. An individual only has to have 1 one copy of the dominant allele (from just one parent) for it to show. An individual with one dominant and one recessive allele for a gene are generally considered “carriers” of the recessive allele: the recessive allele is there, but the recessive phenotype is not. Recessive alleles For a recessive allele to produce a recessive phenotype, the individual must have two copies, one from each parent. E.g. the allele for wrinkled seeds is recessive to the allele for round seeds. Genotype vs phenotype The term genotype describes the genes/alleles an individual has for a particular trait. When discussing an organism’s genotype for a particular trait, we use capital letters to describe a dominant allele and lower case letters to describe recessive alleles. The observable trait that results from gene expression is called its phenotype. Example: Freckles Two possible phenotypes for freckles are: Has freckles No freckles The possible alleles for freckles are: F (dominant) = has freckles f (recessive) = No freckles Question: Using F and f, what are the possible genotype and phenotype combinations for the freckles alleles? Answer: FF (freckles) Ff (freckles) ff (no freckles) Example: Hair colour Question: Red hair colour is recessive to brown colour. If Ron has red hair; a) What is his genotype? bb b) What are the genotypes of his parents? bb (for those of you know know the books Ron’s parents both have red hair) Punnett Squares Punnett squares are used in genetics to help predict the possible genotypes and phenotypes of offspring. They show all the possible combinations of alleles that can result when two organisms are crossed. Remembering: due to independent assortment in meiosis the allele that each parent passes on is based on chance, just like tossing a coin. Punnett squares Complex inheritance Non-mendelian genetics Rather than following the rules of Mendelian inheritance of dominant and recessive genes, complex traits follow different patterns of inheritance that may involve multiples genes and other factors. For example, Incomplete dominance Codominance Multiple alleles Incomplete dominance Incomplete dominance results in a phenotype that is a blend of a heterozygous allele pair. E.g. In snapdragon plants If a homozygous red flower parent is crossed with a homozygous white parent, all offspring will produce pink flowers. Take note of how the genotypes are written Incomplete dominance problem Determine the genotype and phenotype ratios of a cross between two pink (CRCW) snapdragon plants. Draw a punnett square to show your working. Incomplete dominance problem 2 Curly hair is incomplete dominant to straight hair. Determine the probability of a person with straight hair (HSHS) and a person with wavy hair (HCHS) having a child with curly hair. Answer: 0% HH S S H H C S HS HS HC HCHS HCHS HS HSHS HSHS Asexual vs. Sexual Reproduction 74 Asexual Reproduction Requires only one parent Offspring have 100% the same chromosomes as the parent. In other words, the offspring are exact “copies” of the parent. Most unicellular organisms reproduce this way. 75 Asexual Reproduction: Types Example: Binary Fission Occurs in bacteria and protists Binary fission is a form of asexual reproduction where every organelle is copied and the organism divides in two. 76 Asexual Reproduction Example: Budding Occurs in Hydra Budding is a means of asexual reproduction whereby a new individual develops from an outgrowth of a parent, splits off, and lives independently. 77 Asexual Reproduction Example: using Spores This occurs in fungi, algae and protozoa Airborne cells that are released from the parent. They are enclosed and developed when the environment is right 78 Asexual Reproduction Example: Regeneration Regeneration occurs when a body part has broken off and the organism grows a new one. 79 Asexual Reproduction Example: Fragmentation Fragmentation is a means of asexual reproduction whereby a single parent breaks into parts that regenerate into whole new individuals. 80 Asexual Reproduction Parthenogenesis is a type of asexual reproduction in which the offspring of some species develops from the egg or female gamete without first being fertilised by the male gamete. 81 Asexual Reproduction Examples of organisms that reproduce asexually Hydra Sea Star Strawberry Archaebacteria Eubacteria Euglena Paramecium Yeast 82 Sexual Reproduction All the members of the Animal Kingdom Fish Mammals Amphibians Birds Reptiles Insects Crustaceans 83 Sexual Reproduction Requires two parents that each share ½ of the genetic information. Offspring share the characteristics of each parent. 84 Advantages vs Disadvantages of Asexual Reproduction Advantages Disadvantages Asexual reproduction Same DNA being produces more offspring Asexual reproduction takes less time Only one parent involved. No searching for mates Requires less energy passed down NO GENETIC VARIATION IN THE OFFSPRING If parent has genetic disease offspring will have it too 85 Advantages vs Disadvantages of Sexual Reproduction Advantages Disadvantages Variation in offspring  Organism is more Requires two protected because of genetic variation organisms. Must find a mate requires more cellular energy More time required for offspring development 86