Characteristics of living things
Name four characteristics shared by all living organisms.
Any four of: nutrition, respiration, excretion, response to surroundings/sensitivity, movement, control of internal conditions, reproduction, growth and development.
Name three structures found in both plant and animal cells and give the function of each.
Any three: nucleus – contains genetic material and controls cell activities; cytoplasm – site of many chemical reactions; cell membrane – controls movement of substances into and out of the cell; mitochondria – site of aerobic respiration; ribosomes – site of protein synthesis.
Put these levels of organisation in order from smallest to largest: organ, cell, organelle, system, tissue.
Organelle → cell → tissue → organ → system
Which four groups of organisms are classified as eukaryotes in this topic?
Plants, animals, fungi and protoctists.
A plant bends and grows towards a source of light. Which two characteristics of living organisms are demonstrated?
Response to surroundings and growth/development (movement may also be accepted if appropriately explained).
Name three structures normally found in plant cells but not animal cells, and give the function of each.
Cell wall – made of cellulose and provides support/strength; chloroplasts – contain chlorophyll and are the site of photosynthesis; large permanent vacuole – contains cell sap and helps keep the cell turgid.
What is a tissue, and give one example of a tissue in the human body.
A tissue is a group of similar specialised cells working together to perform a particular function. Example: muscle tissue, nervous tissue, epithelial tissue.
I am usually made of hyphae, my cell walls contain chitin, and I cannot photosynthesise. Which group do I belong to, and how do I obtain nutrients?
Fungi. They use saprotrophic nutrition: digestive enzymes are secreted onto food and the soluble products of digestion are absorbed.
A human maintains a body temperature of approximately 37°C even when the environmental temperature changes. Which characteristic of living organisms does this demonstrate, and why is it important?
Control of internal conditions (homeostasis). It maintains suitable internal conditions for processes such as enzyme-controlled reactions.
A muscle cell contains many more mitochondria than a typical skin cell. Explain why this adaptation is useful.
Muscle cells require large amounts of energy for contraction. Mitochondria are the site of aerobic respiration, which releases energy, so having many mitochondria allows a high rate of respiration to meet the cell's energy demands.
The heart contains muscle tissue, nervous tissue and blood. What level of organisation is the heart? Explain your answer.
An organ. It is made of different tissues working together to perform particular functions.
Give three structural differences between a typical plant cell and a bacterial cell.
Plant cells have a nucleus, cellulose cell wall, and may contain chloroplasts. Bacteria have no nucleus, their cell wall is not cellulose, and they do not have chloroplasts. Bacteria also have circular DNA and may contain plasmids.
A student says: “Excretion and egestion are the same thing because both remove waste from the body.” Explain why the student is incorrect.
Excretion is the removal of waste products of metabolism, such as carbon dioxide and urea. Egestion is the removal of undigested/unabsorbed food from the digestive system, so it is not excretion.
Almost every cell in a person's body contains the same genetic information, yet a nerve cell looks and functions very differently from a muscle cell. Explain how this is possible.
Through cell differentiation, cells become specialised for particular functions. Different genes are expressed/activated in different cells, causing them to produce different proteins and develop different structures. This allows cells with the same DNA to become specialised for different functions.
Starting with a muscle cell, describe how it contributes to the organisation of the circulatory system. Use the appropriate levels of organisation.
Muscle cells → cardiac muscle tissue → heart → circulatory system. Cells form tissues, different tissues form an organ, and organs work together in an organ system.
An unknown microscopic organism is single-celled, has a cell membrane and cell wall, contains circular DNA and plasmids, but has no nucleus. Identify the group it belongs to and explain how you know it is not a eukaryote.
It is a bacterium/prokaryote. It has no nucleus; its DNA occurs as a circular chromosome free in the cytoplasm, and it may contain plasmids. Eukaryotic cells have their genetic material contained within a nucleus.
A dormant seed does not visibly move, grow or reproduce. Explain why it can still be classified as a living organism.
A living organism does not need to demonstrate every characteristic continuously. The seed contains living cells and can respire at a very low rate, and under suitable conditions it can germinate, grow, develop and eventually reproduce.
Stem cells could be used to replace damaged nerve cells in a patient. Give two potential advantages and two potential disadvantages of using stem cells in medicine.
Advantages: stem cells can differentiate into specialised cells and could replace damaged cells/tissues; they may treat conditions that currently have limited treatments. Disadvantages: transplanted cells may be rejected by the immune system; cells could divide uncontrollably and form tumours; embryonic stem cells also raise ethical concerns because obtaining them can involve destruction of an embryo.
A student says: “The stomach and the digestive system are at the same level of organisation because they both help with digestion.” Evaluate this statement and correct it.
The statement is incorrect. The stomach is an organ, made of different tissues working together. The digestive system is an organ system, made of several organs working together, including the stomach, intestines, liver and pancreas.
Scientists discover a microscopic infectious particle containing RNA surrounded by a protein coat. It has no cytoplasm or cell membrane and can only reproduce after entering a host cell. Is it a bacterium, protoctist or virus? Justify your answer and explain why it is not considered a living organism.
surrounded by a protein coat. It has no cytoplasm or cell membrane and can only reproduce after entering a host cell. Is it a bacterium, protoctist or virus? Justify your answer and explain why it is not considered a living organism.It is a virus. Viruses have no cellular structure, contain either DNA or RNA surrounded by a protein coat, and can reproduce only inside living host cells. They are not considered living organisms because they cannot independently carry out the life processes or reproduce outside a host cell.