Biology 30 Defence Strategies Behavioural, Structural, and Physiological Adaptations to Defend Against Pathogens, Predators and Disease Archaea: Do not have many defenses against predators. For a long time scientists did not know if archaea got eaten, but recently it was found that Deep-sea worms living near Costa Rica and off the western United States like to munch on single-celled Arachaea. Protists: There are really only two issues that protists have to face: o Other protists eat each other, reducing the population of protists. o Different types of medicines are made by doctors or scientists to kill protists in the Human Body. Protists do not have good defenses for either of these issues. Eubacteria: Most bacteria associated with foodborne infections (e.g., some E. coli, Salmonella, Listeria monocytogenes) can survive under diverse conditions, both inside and outside of the host. To ultimately cause human infection, a foodborne pathogen must first survive transit in food or water, which is hard since food destined for consumption in the United States is treated to control or eliminate microbial contaminants. Following ingestion in humans, the bacterium must survive human bodily defenses that include gastric acid (ranging from [ph 2.5 4.5]), bile salts, and organic acids within the gastrointestinal tract. To survive these extreme conditions bacteria must sense the changes and then respond with appropriate alterations in gene expression and protein activity. Fungi: Fungi are a good source of nutrients for fungivores (organisms that primarily feed on fungi). Most fungivores are insects but there are also some small mammals (northern flying squirrel). o Fungivores present a threat to their survival. How do they defend themselves from attack? o Produce chemicals (toxins) to deter fungivores from eating them. o Sometimes these toxins, while harmful to the organisms against which they are produced, can be helpful to others. Ex: most widely used antibiotic, namely penicillin, is a toxin produced by Penicillium fungi when their growth is restrained in stressful environments.
Plants: Plant cells are not able to move, so every single cell must be able to defend itself against attack from invading pathogens like fungi and bacteria. Plants have developed two strategies to deal with these invaders. The first line of defense occurs when plant cells detect the presence of some sort of foreign invader (by detecting general characteristics such as the flagella of bacteria or the chitin found in fungi cell walls) and alert surrounding cells by releasing molecules that tell other cells to amp up their defenses. o For example, alerted plant cells may secrete molecules that are harmful to invaders or build up their cell walls for extra protection. The second line of defense exists to protect plants from sneakier invaders. Some pathogens have figured out how to disable the plant's first line of defense. When plant cells recognize that they are being attacked, they fight back. Just as pathogens have evolved to disable plant defenses, plants have evolved to be able to recognize these disabling attacks and counter them. For example, one of the signs of a plant activating the second line of defense is something called the hypersensitive response (HR). Basically, plant cells right around an infection site will kill themselves to stop a pathogen from spreading throughout the plant. This prevents pathogens from getting access to things that they need (like water and nutrients) and usually stops the infection! You have probably noticed this phenomenon on leaves in your backyard! Once the HR has been triggered, plant tissues may become highly resistant to a broad range of pathogens for an extended period of time. This phenomenon is called systemic acquired resistance (SAR) and represents a heightened state of readiness in which plant resources are mobilized in case of further attack. o Researchers have learned to artificially trigger SAR by spraying plants with chemicals called plant activators. These substances are gaining favor in the agricultural community because they are much less toxic to humans and wildlife than fungicides or antibiotics, and their protective effects can last much longer. For mechanical damage caused by insects plants have developed surveillance systems designed to recognize insect pests and respond with specific defense mechanisms. Plants can distinguish between general wounding and insect feeding by the presence of chemicals contained in the saliva of chewing insects. In response, plants may release volatile organic compounds (VOCs). o These chemicals may repel harmful insects or attract beneficial predators that prey on the destructive pests. o For example, wheat seedlings infested with aphids may produce VOCs that repel other aphids. o Lima beans and apple trees emit chemicals that attract predatory mites when damaged by spider mites, and cotton plants produce volatiles that attract predatory wasps when damaged by moth larvae The cell wall is a major line of defense against fungal and bacterial pathogens. It
provides an excellent structural barrier that also incorporates chemical defenses that can be activated when the cell detects the presence of potential pathogens. All plant cells have a primary cell wall, which provides structural support and is essential for turgor pressure, and many also form a secondary cell wall that develops inside of the primary cell wall after the cell stops growing. o Cutin, suberin, and waxes are fatty substances that may be deposited in both primary or secondary cell walls and outer protective tissues of the plant body, including bark. Idioblasts ( crazy cells ) help protect plants against herbivory because they contain toxic chemicals or sharp crystals that tear the mouthparts of insects and mammals as they feed. Pigmented cells often contain bitter-tasting tannins that make plant parts undesirable as a food source. Young red wines often contain high levels of tannins that give wine a sharp, biting taste. Sclereids are irregularly-shaped cells with thick secondary walls that are difficult to chew. o EX: the rough texture of pear fruit (Pyrus spp.) is caused by thousands of sclereid stone cells that can abrasively wear down the teeth of feeding animals. o Stinging nettles (Urtica dioica) produce stinging cells shaped like hypodermic needles that break off when disturbed and inject highly irritating toxins into herbivore tissues. REMEMBER: All of the things that are helping plant cells to protect themselves are the PROTEINS inside! Proteins are the tools that cells have to work with and perform cell functions. Different proteins can help in different ways. o Proteins are sometimes hard to visualize because they are very small and look different depending on what their job is. o As an example, to the right is the structure a protein that you may be familiar with. Hemoglobin is found in our red blood cells and its job is to carry oxygen from the lungs to the rest of the body. It may just look like a jumble of lines - but the way that each individual protein is formed (out of its building blocks - amino acids!) will make it be able to perform different jobs! http://www.apsnet.org/edcenter/intropp/topics/pages/overviewofplantdiseases.aspx
Animals: Dealing with Pathogens: The Immune System Pathogens include two main types: 1. Bacteria a. Ex: pneumonia, chlamydia, food poisoning, pink eye b. These are prokaryotic cells (no organelles) 2. Virus a. Ex: HIV, influenza, common cold, HPV, chicken pox, small pox b. Small infectious agent that replicated only inside the living cells of other organisms can infect all life forms including plants, animals, and bacteria c. Consists of genetic info (DNA or RNA) surrounded by a protective protein coat called a capsid (sometimes also surrounded by an envelope of lipids) Immune system has two main parts: 1. Innate Defenses (nonspecific immunity) a. Not aimed at a specific pathogen and has no memory b. Has two parts c. First line of defense: i. Surface membrane acts as a barrier (physical and chemical) 1. Skin often has acidic secretions 2. Mucous membrane lines all body cavities open to exterior and contains lysozyme (acidic) and trap foreign particles 3. Stomach lining secretes hydrochloric acid d. Second line of defense: i. Natural killer cells 1. group of white blood cells (lymphocytes) that can kill cancer cells, virus-infected body cells, and other nonspecific targets ii. Inflammatory response (triggered when the body is injured) 1. Injured body cells release inflammatory chemicals (histamine and kinins) that dilate blood vessels and cause them to become leaky (called edema), activate pain receptors, attract white blood cells that fight infections. 2. Causes redness, heat, swelling, and pain.
iii. Phagocytes (cell that engulfs and gets rid of bacteria) 1. Present in nearly every body organ iv. Antimicrobial proteins 1. Attack microbes and direct or inhibit their ability to reproduce v. Fever 1. Increases body temperature, increases metabolic rate (increases the repair processes) and causes zinc and iron to be taken up by the liver. 2. Adaptive Defenses (specific immunity) a. Aimed at specific pathogens must be primed by an initial exposure to a foreign antigen before it can protect the body from the invader. b. Results in highly specific resistance to disease (immunity!) has a memory c. Is not restricted to initial infection site d. This is also known as the third line of defense Characteristics Innate Immunity Adaptive immunity Presence Innate immunity is something already Adaptive immunity is created in response present in the body. to exposure to a foreign substance. Specificity Non-Specific Specific Response Fights any foreign invader Fight only specific infection Response Rapid Slow (1-2 weeks) Potency Limited and Lower potency High potency Inheritance Innate type of immunity is generally inherited from parents and passed to offspring. Adaptive immunity is not passed from the parents to offspring, hence it cannot be inherited. Memory Cannot react with equal potency upon Adaptive system can remember the specific repeated exposure to the same pathogen. pathogens which have encountered before. Used Against For microbes Microbes and non-microbial substances called antigens Memory No memory Long term memory Speed Faster response Slower response Composition Example The innate immune system is composed of physical and chemical barriers, phagocytic leukocytes, dendritic cells, natural killer cells, and plasma proteins. White blood cells fighting bacteria, causing redness and swelling, when you have a cut. Adaptive immune system is composed of B cells and T cells. Chickenpox vaccination so that we don t get chickenpox because adaptive immunity system has remembered the foreign body.
Dealing with Predators: Primary Defenses: Primary defenses make it less likely that there will be a meeting between the predator and the prey. In many cases this means the predator has not noticed or recognized the prey. If the prey is good to eat, it must either make itself scarce, or it must look as though it is not good to eat. o Typically animals do this through hiding, camouflage, or mimicking another organism that is foul-tasting. Other prey has more active defences. These are usually one of two kinds: o the animal has a chemical defence o the animal is protected by spines or stingers. Dealing with Predators: Secondary Defences: There are a number of other successful defence techniques that certain animals can use: o Withdraw to a prepared retreat. Ex: turtle hiding in shell o Flee run or fly away. Animals will run in straight lines (if fast) or zig zag (if slow). o Bluff pretend to be threatening. o Play dead Many vertebrate predators reject dead animals Ex: opossum o Deflect the attack or distract Butterflies have small targets near edges of wings in non-essential part of body. Cuttlefish squirt out ink then turn and flee o Fight back Large herbivores often carry weapons (elephant, deer, rhinoceros) Bombardier beetles squirt hot poisonous liquids o Band together Many animals use defensive group tactics