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Unlock This CourseCells are the basic building blocks of all life on Earth, including the incredible diversity of organisms found in marine environments. From tiny phytoplankton to massive whales, every marine organism is made up of cells that have evolved specific structures to help them survive in the ocean. This review session will help you consolidate your understanding of cell biology and prepare for assessments.
Key Definitions:
Found in bacteria and archaea, these simple cells have no nucleus. Their genetic material floats freely in the cytoplasm. Many marine bacteria are prokaryotes, including those that form the base of ocean food webs and those living in extreme environments like deep-sea vents.
Found in plants, animals, fungi and protists, these complex cells have a nucleus containing their DNA. Most marine organisms you can see with the naked eye are eukaryotes, from seaweed to fish to marine mammals.
Understanding the differences between plant and animal cells is crucial for marine science, as marine ecosystems contain both plant-like organisms (such as algae) and animals. Each type of cell has evolved specific structures to meet their different needs.
Animal cells, including those found in marine animals like fish, crabs and whales, have several key organelles that work together to keep the cell alive and functioning.
Controls cell activities and contains DNA. In marine animals, this genetic information determines everything from body shape to behaviour patterns.
Powerhouses of the cell that produce energy (ATP). Marine animals often have many mitochondria to fuel their swimming and other activities.
Make proteins needed for growth and repair. Essential for producing enzymes that help marine animals digest food and function properly.
Plant cells, including those in marine algae and seagrasses, have additional structures that animal cells don't have. These extra organelles help them make their own food and maintain their shape.
Contain chlorophyll and carry out photosynthesis. Marine plants use these to capture sunlight and produce food, forming the base of ocean food chains.
Provides structure and protection. Helps marine plants like kelp grow tall and withstand ocean currents and waves.
Stores water and maintains cell pressure. Helps marine plants stay rigid and upright in the water column.
Diatoms are single-celled marine organisms that are incredibly important to ocean ecosystems. These microscopic plants have beautiful glass-like cell walls made of silica and contain chloroplasts for photosynthesis. They produce about 20% of the world's oxygen and form the base of many marine food webs. Their unique cell structure allows them to float in the water column and efficiently capture sunlight, making them perfectly adapted to marine life.
Marine organisms have evolved amazing cellular adaptations to survive in the ocean environment. These adaptations help them deal with challenges like salt water, pressure, temperature changes and finding food.
Living in salt water creates special challenges for cells. Marine organisms have developed various strategies to maintain the right balance of water and salts in their cells.
Saltwater fish constantly lose water through their gills and skin. Their cells have special mechanisms to pump out excess salt and retain water. Their kidneys are highly efficient at conserving water while removing waste.
Marine plants like seagrasses have cells that can tolerate high salt concentrations. They often have special salt glands that remove excess salt from their tissues.
Deep-sea organisms face enormous pressure that would crush surface-dwelling creatures. Their cells have special adaptations to function under these extreme conditions.
Deep-sea organisms have cells with flexible membranes that don't collapse under pressure. They also produce special proteins that maintain their shape and function in high-pressure environments. Some have gas-filled organs that help them control their buoyancy.
Many marine organisms can produce their own light through bioluminescence, often with the help of symbiotic bacteria. These bacteria have special organelles called photophores that contain the chemicals needed to produce light. The anglerfish uses bioluminescent bacteria in a lure to attract prey, while some squid use light-producing bacteria for camouflage. This is a perfect example of how cellular adaptations can create amazing survival strategies in the marine environment.
To succeed in cell biology assessments, you need to understand not just what each organelle does, but how they work together and how they're adapted for different environments, especially marine ones.
Examiners often test your ability to apply knowledge rather than just memorise facts. Here are the main skills you need to develop:
You might be asked to identify cell structures in diagrams or microscope images. Practice labelling diagrams of both plant and animal cells and be able to explain what each part does.
Be ready to compare different types of cells or explain how cell structure relates to function. For example, why do muscle cells have lots of mitochondria, or how are marine plant cells different from land plant cells?
Based on the iGCSE syllabus, here are the topics most likely to appear in your assessments:
Coral polyps are tiny marine animals whose cells have formed a remarkable partnership with algae called zooxanthellae. These algae live inside the coral's cells and use photosynthesis to produce food, which they share with the coral. In return, the coral provides the algae with protection and nutrients. This cellular partnership is so successful that it has created some of the most diverse ecosystems on Earth - coral reefs. However, when water temperatures rise, the partnership breaks down, leading to coral bleaching.
The best way to prepare for assessments is through active practice. Try drawing and labelling cell diagrams from memory, explaining the function of each organelle and thinking about how marine organisms use their cellular adaptations to survive in the ocean.
Before your assessment, make sure you can: