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The big ideas in biology transcend all its individual topics. As much as possible these five concepts need to make explicit appearances in every topic and should be planned for. Below I discuss how I include the big ideas in my Year 7 biology curriculum.
As expert biologists we have a vast bank of knowledge to draw upon and understanding how concepts are linked in biology is easy. Novices on the other hand, like our fresh Year 7 students, will struggle. If we are not careful, students may come to see biology as a collection of unconnected topics in which they need to remember a list of components (think lists of organs, specialised cells, labels for food-web members, or parts of a plant).
Biology isn't a set of horizontal structures but vertical in nature with knowledge that is built hierarchically. This is more visible in chemistry, for example, as most secondary-level topics will construct upon the students' knowledge of particles in ever more detail.
The problem we have in secondary biology is that the field appears so vast with seemingly unconnected disciplines: ecology, botany, zoology, animal physiology, microbiology, etc. There simply isn't enough time in secondary school to address them all as much as a biologist would wish. Plants are generally over shadowed in current anthropocentric biology courses, and microorganisms, as paramount as they are, appear sparingly. This lack of time for content can leave certain topics stranded as the understanding of human biology grows.
As students build more knowledge and connections on human biology, will they be able to generalise this knowledge to other areas of biology? This is difficult, unless our curriculum is conducive to understanding that biology is built upon deep principles that bind all the biological sciences.
The big ideas in biology
Young man, in mathematics you don't understand things. You just get used to them.
This is the famous quote of John von Neumann when replying to a student. I often think about how this relates to the big ideas in biology. They represent abstract ideas, and they will take years of learning and practising in biology for students to fully appreciate their deep ramifications and connectedness. This is exactly why they should appear explicitly and constantly throughout our biology curriculum, so that students eventually just get used to them. They become biology, and students anticipate them when entering a novel biological science topic.
What do the big ideas mean to me? Here is a brief summary:
Information:
DNA, inheritance
Phenotype, genotype
Energy & matter:
Anabolism & catabolism
The flow of energy through cells, organisms, populations, and ecosystems
The cycling of matter in ecosystems
Organisation:
The levels of organisation in biology, from molecules, organelles, cells, up to ecosystems.
Structure and function
Emergent properties & systems
Homeostasis:
Maintenance of conditions at various levels of organisation (in cells, in organisms, in ecosystems)
Maintenance of disequilibrium & gradients
Feedback
Evolution:
Natural selection
Speciation
Common ancestry
Year 7 students need early, and consistent exposure to, and explicit discussion of, the big ideas. Every topic that is planned should consider how these big ideas will be explicitly presented.
Here's how I represent the big ideas during my four biology topics of Year 7 (as I also teach chemistry and physics, these topics will not necessarily be consecutive but they do come in this order):
1. Cells to systems
Organisation:
This is the main focus of the topic. I begin with unicellular organisms and consider how they obtain oxygen and nutrients by diffusion (necessitating the prior study of particle theory).
From here we study multicellular organisms and how they are organised (organelles, cells, tissues, organs, systems). We consider how systems are a required organisation of large multicellular organisms due to diffusion constraints. It is for this reason that I begin with unicellular organisms and not systems; so that students understand why systems are a requisite of larger organisms.
Emergent properties is an important feature of our study of multicellular organisms. It is worth discussing how a human brain may be composed of 300 billion cells and only through 'working together' can these cells enable thought.
Information:
I introduce the students to the nucleus in the first lesson. The nucleus is not referred to as 'the brain of the cell', nor is DNA described as 'instructions'. This may instil the misconception that one piece of DNA can somehow 'know' how to compile a multicellular organism , or equally, that a single cell can think.
DNA is defined as 'information to build cells' and this combines with the big idea of organisation when we study how 'cells working together form tissues'.
Energy & matter:
We begin this idea early when we consider the needs of a unicellular organism, it requires energy to carry out its functions, and molecules to build its cell. The latter point here is important as students often find this surprising and it is not intuitive to them. This is reinforced later as we study the digestive, respiratory, and circulatory systems, and how these work together (organisation) to ensure that cells of the body meet their needs of energy and matter.
At this level, and for the moment, I keep this to 'food & oxygen' and 'waste carbon dioxide'. We focus on the function of the mitochondria and learn how cells need energy to function or they will die. They also come to learn that they build their body cells from the particles in the food they eat.
Homeostasis:
As we study the digestive, respiratory, and circulatory systems, I explicitly talk about the importance of maintaining oxygen levels and the removal of carbon dioxide. We talk about 'keeping the balance' and that in biology this is called homeostasis.
Evolution:
The fundamentals of natural selection are quite intuitive and easily recognised by Year 7 students. The details can wait, but by then, they will be accustomed to the idea of the differential survival of organisms and 'who passes on their DNA'. In this topic, we talk about evolution when we consider the advantages of being multicellular compared to unicellular.
2. Human reproduction
Organisation:
It is important that students do not just learn a list of components, but consider if each part is a tissue, organ, or system, and individual cells should be considered. The egg and sperm cells take centre stage as we discuss their adaptations (structure & function), but we learn about ciliated cells in the oviduct also.
Information:
I spend the first lesson just talking to the students about why life reproduces: DNA that does not intend on being passed on will be lost. Only the DNA that intends on being passed on exists in life. We are all being manipulated by our DNA to reproduce. I give them a simple version of the Disposable Soma Theory.
The details on chromosomes can wait, for now students understand easily that 'you inherit one set of DNA' from each parent.
Energy & matter:
This is covered again when comparing the egg cell to the sperm cell, their adaptations and energy requirements. Later in the topic we consider why semen contains 'sugar'.
Homeostasis:
In the first topic students may get the sense that homeostasis is a goal for allowing the body to grow, but the ultimate goal of the body is to reproduce. We learn this here and discuss then how the other systems work to allow the reproductive system to produce gametes.
Evolution:
In this topic the big ideas of information and evolution are discussed heavily in the first lesson but are then reinforced continually throughout. One salient point to be made explicit is why so many sperm are released during ejaculation and why the journey to the oviduct is so difficult.
3. Food webs
As I teach in Spain, I base this topic within the context of the Iberian Lynx.
Energy & matter:
This big idea is very salient in this topic. We constantly refer to the flow of energy in the food web, its origins, photosynthesis, and then the loss of energy via heat.
Later in the topic we move to consider the movement of matter: How decomposers 'recycle minerals' and how carbon dioxide is cycled back to the plants via the air.
At the end of the topic as we consider reasons for the major decline in the Iberian Lynx we look at the extensive agricultural land in Andalucía, the loss of producers (and energy) from the Lynx's food web, but also the loss of 'minerals' from the soil and the use of fertilisers.
We consider which vertebrates are endotherms (birds & mammals), and how this affects their feeding patterns and energy requirements.
Finally, the interaction between photosynthesis and cell respiration is studied.
Homeostasis:
In this topic we consider predator-prey population relationships, the importance of apex predators on controlling herbivore populations, and discuss them explicitly using the word homeostasis. We also learn about decomposers and how minerals are cycled. Generally food webs tend to maintain homeostasis unless humans start interfering.
Information & evolution:
Information and evolution are again jointly present in this topic. We learn about predator and prey adaptations and consider how thousands of years of predator and prey relationships has shaped their bodies.
Organisation:
Structure and function is important here when we learn about predator and prey differences, especially the location of their eyes.
We look at adaptations for endothermic mammals in the arctic and the desert. Nicely, we get to compare the Iberian lynx to the Canada Lynx.
We consider how surface area to volume ratio (with Year 7 I refer to it as their 'surface area for their body size') affects heat loss and how mammals in the arctic and desert differ in this aspect. Surface area to volume ratio is a huge component of this big idea and a hugely important concept for all of biology, therefore it is important to begin discussing this early and often.
4. Variation
Charles Darwin spent nearly a decade compiling data on variation in species (mainly barnacles) to support the pending publication of his theory. Before that people hadn't thought much of variation and generally thought members of species to be, well, all alike. It is a fundamental component of natural selection, thus this is not just a short topic looking only at genetic vs environmental inheritance, but also how this relates to evolution.
Information:
Here we can directly and explicitly, for the first time, relate DNA to phenotype when discussing genetic and environmental inheritance patterns. I also give the students some questions on identical twins, and we discuss banana monocultures and their risk of disease.
Evolution:
This is an important topic for this big idea. To make things simpler at this level, I have a lesson adapted from the resources from HHMI Biointeractive on the variation in coat colours of the rock pocket mouse. Students count mice on pictures to visualise how the dark fur prevails on the (new) dark volcanic rocks, and the light fur on the light sand and how population numbers change over time.
Energy and matter:
Energy balance in diet is considered when we talk about height and weight tendencies in humans and whether this can be attributed to genetics, the environment, or both.
Homeostasis:
The rock pocket mouse example of variation is considered within its food web and how variation enabled the species to survive and maintain its populations despite a change in the environment.
Organisation:
Essentially, this is where we can explicitly relate DNA mutations to changes in phenotype, and it is important to discuss how this holds a consequence at each level of organisation, from DNA, to the cells, to tissues, etc.
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Christian Moore-Anderson
@CMooreAnderson (twitter)