Characteristics of living organisms
State four characteristics of living organisms. (4)
Any four of:
Nutrition
Respiration
Excretion
Response to surroundings (sensitivity)
Movement
Control of internal conditions
Reproduction
Growth and development
List three organelles found in a plant cell but not in an animal cell. Describe the primary function of one of these organelles.
The three organelles are the cell wall, chloroplasts, and a large central vacuole.
Function: (Example: Chloroplasts) These are the site of photosynthesis, where light energy is absorbed by chlorophyll to produce glucose for the plant.
Name the chemical elements that are present in all carbohydrates, proteins, and lipids. Which additional element is always found in proteins but not in the other two?
All three molecules contain Carbon (C), Hydrogen (H), and Oxygen (O). Proteins also contain Nitrogen (N).
Define osmosis and state whether it is a passive or active process.
Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential across a selectively permeable membrane. It is a passive process because it does not require energy from respiration.
List the seven components of a balanced diet and identify one specific food source for Vitamin D and one for Iron.
A balanced diet includes carbohydrates, proteins, lipids (fats and oils), vitamins, minerals, water, and dietary fibre.
Vitamin D source: Oily fish or eggs.
Iron source: Red meat or spinach.
(a) Explain what is meant by:
(i) Respiration
(ii) Control of internal conditions
Respiration is the chemical process that releases energy from food (glucose) in cells.
(ii) Control of internal conditions (2)
Answer:
This means maintaining a constant internal environment (homeostasis), such as stable body temperature or water content.
Both animal and plant cells contain mitochondria and ribosomes. Compare the roles of these two structures in maintaining cell function.
Mitochondria: The site of aerobic respiration. They release energy (ATP) from glucose to power cellular processes.
Ribosomes: The site of protein synthesis. They translate genetic information into proteins (such as enzymes or hormones) needed by the cell.
Key Difference: Mitochondria provide the energy required for the ribosomes to build those proteins.
Large biological molecules are made up of smaller basic units. State the specific building blocks (monomers) used to form starch, proteins, and lipids.
Starch: Simple sugars (specifically glucose).
Proteins: Amino acids.
Lipids: Fatty acids and glycerol.
Describe one similarity and one major difference between diffusion and active transport.
Similarity: Both processes involve the movement of substances into or out of cells through the cell membrane.
Difference: Diffusion involves particles moving down a concentration gradient (high to low) without energy, whereas active transport moves particles against a concentration gradient (low to high) using energy.
Describe the process of peristalsis and explain its importance in the digestive system.
Peristalsis is the series of wave-like muscle contractions (longitudinal and circular muscles) that occur in the walls of the alimentary canal. Its role is to squeeze and move food (bolus) through the gut, such as from the mouth to the stomach via the oesophagus.
(a) State two features of plants.
Store carbohydrate as starch or sucrose
(b) State two features of animals.
(c) Give one difference between fungi and plants.
(a) Cells contain chloroplasts
Cells have cellulose cell walls
Multicellular
Store carbohydrate as starch or sucrose
(b) Multicellular
No cell walls
No chloroplasts
Store carbohydrate as glycogen
Usually show nervous coordination and movement
(c) Fungi do not carry out photosynthesis, whereas plants do.
OR
Fungi have cell walls made of chitin, while plants have cellulose cell walls.
Explain the process of cell differentiation. Why is it essential for a multicellular organism to have specialized cells rather than a collection of identical cells?
Cell differentiation is the process by which a cell changes to become specialized for its job by developing specific sub-cellular structures.
Importance: Multicellular organisms are complex. Specialized cells (like nerve cells for signaling or muscle cells for movement) allow for a division of labor, making the organism much more efficient than if every cell tried to perform every function simultaneously.
A student is testing a food sample for the presence of protein and glucose. Describe the chemical tests they should use, including the names of the reagents and the positive result for each.
Protein: Use Biuret reagent. A positive result is a color change from blue to purple/mauve.
Glucose: Use Benedict’s solution and heat the mixture in a water bath. A positive result is a color change from blue to green, yellow, or brick-red (depending on concentration).
In a practical investigation using non-living systems, a Visking tubing bag filled with concentrated sugar solution is placed in a beaker of pure water. Predict and explain what will happen to the volume of the liquid inside the bag.
The volume of liquid inside the bag will increase. This is because water molecules will move from the beaker (high water potential) into the bag (low water potential) by osmosis. The sugar molecules are too large to move out through the membrane.
Complete the following information regarding digestive enzymes: Name the enzyme that breaks down starch, the enzyme that breaks down proteins, and identify the resulting "smaller basic units" for each.
Starch: Broken down by amylase (and maltase) into glucose.
Proteins: Broken down by proteases into amino acids.
Lipids: (For context) Broken down by lipases into fatty acids and glycerol.
(a) Describe three structural features of bacteria.
(b) Define the term pathogen. (1)
(c) Name two types of organisms that can act as pathogens.
(a) Single-celled (unicellular)
Have a cell wall
Have cytoplasm
Have a cell membrane
Have plasmids
No nucleus
Contain circular DNA
(b)
A pathogen is a microorganism that causes disease.
(c)
Bacteria
Fungi
Protoctists
Viruses
A scientist is studying a mystery cell under a microscope. They observe a cell wall and a large central vacuole, but no chloroplasts. Identify the cell type and explain why the absence of chloroplasts does not necessarily mean the cell is from an animal.
Reasoning: Animal cells never possess a cell wall or a permanent large vacuole. The absence of chloroplasts is common in plant cells that are not exposed to light, such as root hair cells. Since these cells are underground, they do not perform photosynthesis and therefore do not require chloroplasts.
Explain the role of enzymes as biological catalysts and describe what happens to the "active site" if the temperature increases significantly beyond the enzyme's optimum.
Enzymes speed up metabolic reactions without being used up themselves. If the temperature becomes too high, the enzyme denatures. This means the shape of the active site changes, and it is no longer complementary to the substrate. The substrate can no longer fit, and the reaction stops.
Explain how the distance over which a substance must travel and the concentration gradient affect the rate of diffusion.
Distance: The shorter the distance (e.g., a thin cell membrane), the faster the rate of movement because particles have less far to travel.
Concentration Gradient: A steeper gradient (a larger difference in concentration between two areas) increases the rate of movement as there is a stronger net movement in one direction.
Bile is not an enzyme, yet it is essential for the digestion of lipids. Identify where bile is produced and stored, and explain its two primary roles in the small intestine.
Bile is produced in the liver and stored in the gall bladder.
Role 1 (Neutralisation): It is alkaline and neutralises the hydrochloric acid coming from the stomach, providing the optimum pH for enzymes in the small intestine to work.
Role 2 (Emulsification): It emulsifies lipids, breaking large fat droplets into smaller ones to increase the surface area for lipase enzymes to act upon.
A student observes a microscopic single-celled organism. It contains chloroplasts and a nucleus.
(a) State the kingdom to which this organism most likely belongs.
(b) Give two reasons for your answer.
(c) Explain two differences between this organism and a bacterium.
a) Protoctist.
(b)
It is single-celled.
It contains chloroplasts.
It has a nucleus (eukaryotic).
This organism has a nucleus, whereas bacteria do not (bacteria are prokaryotic).
This organism contains chloroplasts, whereas most bacteria do not.
OR
Bacteria have circular DNA and plasmids, while this organism has DNA enclosed in a nucleus.
Evaluate the advantages and disadvantages of using embryonic stem cells in medical research and treatments.
Advantages: They are pluripotent, meaning they can differentiate into any type of specialized cell. This allows them to treat a wide range of conditions like paralysis (replacing nerve cells) or diabetes (replacing insulin-producing cells).
Disadvantages: There are major ethical concerns as the extraction process usually destroys a human embryo. There is also a risk of rejection by the patient’s immune system or the potential for the cells to divide uncontrollably, causing tumors.
In an investigation into enzyme activity, a student finds that the rate of reaction decreases when the pH is shifted from pH 7 to pH 4. Explain why this change in pH affects the rate of reaction.
Changes in pH alter the chemical bonds within the enzyme. This alters the shape of the active site. Since the active site is no longer the correct shape to fit the substrate, fewer enzyme-substrate complexes can form, leading to a decrease in the rate of reaction. Extreme pH levels will lead to complete denaturation.
Single-celled organisms can rely solely on diffusion for gas exchange, but large multicellular organisms cannot. Use the concept of surface area to volume ratio to evaluate why this is the case.
Single-celled organisms have a large surface area to volume ratio, meaning their outer surface is large enough to supply the small internal volume via diffusion. As an organism increases in size, its volume increases much faster than its surface area, resulting in a small surface area to volume ratio. Consequently, diffusion distance becomes too great to provide oxygen or nutrients to the center of the organism fast enough to sustain life.
The small intestine is the primary site for the absorption of digested food. Explain how the structure of a villus is specifically adapted to maximise the rate of absorption.
Villi are adapted for absorption in three main ways:
Surface Area: The folded shape of the villi (and microvilli on their surface) provides a massive surface area for diffusion and active transport to occur.
Diffusion Distance: The wall of the villus is only one cell thick, creating a very short distance for nutrients to travel into the bloodstream.
Concentration Gradient: Each villus has a rich network of blood capillaries that quickly carry away absorbed glucose and amino acids, and a lacteal to transport fats. This constant movement maintains a steep concentration gradient between the gut and the blood.